London's Ultimate Guide to SaaS Google Ads Agencies

I see this question a lot. You're a SaaS founder in London, probably based somewhere between Shoreditch and Canary Wharf, you've got a great product, maybe some early traction, and now you're looking to pour some fuel on the fire with Google Ads. The problem is, every agency you speak to sounds the same. They talk a good game about "driving traffic" and "brand awareness," show you some flashy e-commerce case studies, and then send over a proposal that feels like it was copied and pasted.

Let's be brutally honest: you're not just struggling to find the right agency. You're struggling because 95% of the agencies out there, even the ones with swanky offices in the City, have absolutely no idea how to properly market a SaaS product. They're used to selling £50 trainers, not a complex B2B solution with a 6-month sales cycle and a five-figure lifetime value. Choosing the wrong partner isn't just a waste of money; it's a waste of time and momentum you can't get back. The key isn't finding a local agency, it's finding one that speaks your language: the language of MRR, churn, and user acquisition cost.

So, why is it so bloody hard to find someone decent?

The London tech scene is booming, which is great. But it also means there's a flood of "digital marketing" agencies popping up, all claiming to be experts in everything. They might be brilliant at getting a local plumber leads or selling fast fashion, but that skillset is almost completely irrelevant to you. B2C e-commerce is about impulse buys and quick conversions. B2B SaaS is a considered purchase, often involving multiple decision-makers, complex onboarding, and a focus on long-term value, not a one-off sale.

An agency that boasts about a "10x ROAS" for a clothing brand is talking about a different sport altogether. For you, Return on Ad Spend is a lagging indicator. What you need to care about right now are leading indicators: Cost per Trial, Cost per Demo, and most importantly, your Customer Acquisition Cost (CAC) in relation to your Lifetime Value (LTV). Most generalist agencies don't even know how to have this conversation. They'll take your money, run some broad match keywords, point them at your homepage, and then wonder why you're not getting sign-ups. It's a fundamental missunderstanding of the business model.

I remember one B2B software client who came to us after burning through £20,000 with a well-known London agency. The agency was proud they’d generated hundreds of "leads." But when we dug in, they were just names and emails from a generic content download. Not a single one had turned into a meeting, let alone a customer. The campaign was a total failure because the agency was optimising for the wrong thing. They were chasing cheap MQLs (Marketing Qualified Leads) instead of focusing on generating PQLs (Product Qualified Leads)—users who are actively using your product and showing buying intent. It's a subtle distinction, but it makes all the difference.

What should I actually be looking for in their case studies?

This is where you can start to separate the experts from the pretenders. Forget the glossy PDFs and look for the numbers that matter to a SaaS business. When you review a case study, you need to be a detective.

First, are they even working with SaaS clients? If their portfolio is all dentists and online boutiques, close the tab. It's not a good fit. You want to see logos you recognise or at least business models that mirror your own. Second, what metrics are they highlighting? If it's all about impressions, clicks, or vague "engagement," that's a massive red flag. Those are vanity metrics. They make agencies look busy but don't translate to business growth.

You want to see case studies that talk about:

• -> Cost Per Acquisition (CPA) or Cost Per Trial: This is the bread and butter. How much does it cost them to get a new user to sign up for a trial or a paid plan? For example, one of our Google Ads campaigns for a software client acquired 3,543 users at a cost of just £0.96 per user. That's a concrete result. Another campaign for a medical job matching platform, we managed to reduce their CPA from a staggering £100 down to just £7. That's the kind of impact a specialist can have.
• -> Lead to Customer Rate: How many of the leads or trials they generate actually convert into paying customers? A good agency understands the entire funnel and cares about the quality of the traffic, not just the quantity.
• -> Scalability: It's one thing to get a few cheap sign-ups. It's another to build a system that can scale from £5k/month in ad spend to £50k/month without the CPA going through the roof. Look for evidence that they can grow with you. A campaign that delivered 45,000+ signups is a good indication of an ability to scale.
• -> Platform Expertise: For B2B SaaS, it's not just about Google Search. Do they have experience with LinkedIn Ads for targeting specific job titles? Have they used YouTube for demonstrating a complex product? We ran a LinkedIn Ads campaign for a software client that brought in leads from B2B decision makers at a $22 CPL. That shows an understanding of which platform to use for which audience.

Essentially, you want to see proof that they've solved the exact problem you're facing for a business just like yours. Vague claims are worthless. Look for specific numbers and outcomes.

How do I know if they understand the maths of my business?

Here's the single biggest test. If you get on a call with an agency and they don't ask you about your Lifetime Value (LTV) and Customer Acquisition Cost (CAC) within the first 20 minutes, they are not the right agency for you. It's that simple.

Running ads without knowing these numbers is like flying a plane without an altimeter. You have no idea if you're climbing or about to crash into a mountain. The real question isn't "How low can my CPL go?" but "How high a CPL can I afford to acquire a truly great customer?" The answer is locked inside your unit economics.

Let's break it down. You need three pieces of data:

• Average Revenue Per Account (ARPA): How much you make per customer, per month.
• Gross Margin %: Your profit margin on that revenue.
• Monthly Churn Rate: The percentage of customers you lose each month.

The calculation is straightforward:

LTV = (ARPA * Gross Margin %) / Monthly Churn Rate

For example, if your ARPA is £500, your gross margin is 80%, and you lose 4% of your customers each month, your LTV is £10,000. (£400 / 0.04 = £10,000).

This £10,000 figure is your truth. It's the maximum potential value of a new customer. A healthy business model often aims for a 3:1 LTV:CAC ratio. In this case, you can afford to spend up to £3,333 to acquire a single new customer. If your sales process converts 1 in 10 qualified trials into a customer, you can afford to pay up to £333 for that trial. Suddenly, a £50 Cost Per Trial on Google Ads doesn't look expensive; it looks like an incredible bargain. This is the maths that unlocks aggressive, intelligent growth. An agency that doesn't live and breathe this stuff will be constantly trying to "lower your costs," potentially by targeting lower-quality users, when they should be focused on finding you more £10,000 customers.

Use the calculator below to get a handle on your own numbers. Before you even speak to another agency, know your LTV. It will completely change the conversation.

What sort of questions should I ask them on the discovery call?

Once you've vetted their case studies and you're confident they understand your business maths, the discovery call is your chance to really test their expertise. Don't let them run a generic sales pitch. You should be the one asking the tough questions. Here are a few to get you started:

• "Our product is quite niche and doesn't have a high search volume for exact-match keywords. How would you approach building a Google Ads strategy to generate leads beyond the obvious terms?"
  A good answer will involve talking about targeting competitor keywords, using broader problem-aware keywords, and leveraging audience targeting on the Display Network and YouTube. A bad answer is "we'll do more keyword research."


• "Walk me through how you'd structure our campaigns to target different personas, for example, the end-user versus the C-level budget holder."
  Their response should cover using different messaging, landing pages, and potentially different platforms (e.g., Google Search for the user with a problem, LinkedIn for the decision-maker). It shows they think about the buyer journey, not just keywords.


• "What's your opinion on our current offer? We're using a 'Request a Demo' call to action."
  This is a test. As we've discussed, "Request a Demo" is often a high-friction, low-value offer. A top-tier agency should challenge this. They should ask why you're not offering a free trial or a freemium plan. They should talk about the importance of getting users into the product (PQLs). If they just accept your current offer without question, they're order-takers, not strategic partners.


• "What metrics will you be reporting on weekly and monthly, and why?"
  You want to hear them talk about business metrics: Cost per Trial, Trial-to-Paid Conversion Rate, CPA, and eventually, LTV:CAC. If they lead with clicks, impressions, or Click-Through Rate (CTR), their priorities are in the wrong place. They should be able to explain exactly how their activity translates into MRR for your business.


• "What do you need from us to be successful?"
  A great agency knows they can't work in a vacuum. They'll ask for access to your analytics, your CRM data, and regular contact with your product/sales team. They'll want to understand your customers deeply. An agency that says "just give us the budget and we'll handle it" is a massive red flag.

The goal of this call isn't for them to sell you, it's for you to determine if they have the specific, nuanced expertise required to grow a SaaS business. It's an interview, and you're the hiring manager.

Are they just Google Ads jockeys, or do they get the whole funnel?

This is a critical point. Driving traffic with Google Ads is only one part of the equation. If that traffic lands on a confusing, low-converting page, you're just pouring water into a leaky bucket. A truly valuable agency partner acts more like a growth consultant. They understand that the ad is just the beginning of the conversation.

They should be asking tough questions about your landing page. Is the value proposition crystal clear within three seconds? Is the headline speaking directly to the "nightmare" problem your ideal customer is facing? Are you using social proof effectively? Is the call-to-action compelling? A specialist agency might even have copywriters or conversion rate optimisation (CRO) experts they can bring in, because they know that a 2% increase in landing page conversion rate can have a bigger impact on your CPA than any amount of keyword tweaking.

Think of the customer journey:

A generalist agency only focuses on the first box. A true SaaS growth partner is obsessed with the entire journey. They know that a brilliant ad campaign pointed at a bad offer is doomed to fail. This is why you must find an agency that has an opinion and isn't afraid to tell you your baby is ugly. Their job is to bring outside expertise to challenge your assumptions and improve your entire acquisition funnel, not just to manage your keywords.

What should my budget and expectations be in the London market?

This is a common question, and the honest answer is: it depends. But it's almost certainly more than you think. London is one of the most competitive markets in the world. Clicks for valuable B2B keywords can be expensive. Trying to get results with a budget of £500 a month is, frankly, a waste of money. You won't get enough data to make intelligent decisions, and you'll get outbid on every meaningful term.

As a rule of thumb, for a serious B2B SaaS campaign on Google Ads, I'd recommend a minimum starting ad spend of £2,000-£3,000 per month. This gives you enough runway to test different campaigns, keywords, and ad copy to find out what works. Anything less and you're just gambling.

In terms of what to expect for your money, here are some very rough ballpark figures for the UK/London market based on our experience:

Remember, these are just averages. We've seen campaigns achieve far better results, like the B2B software campaign I mentioned earlier that generated leads for just $22 (£17-ish), but we've also seen niches where the costs are much higher. The key is to compare these costs to your LTV. If your LTV is £20,000, paying £200 for a qualified lead that has a 1 in 10 chance of closing is a fantastic deal. If you don't know your numbers, you have no way of knowing if your campaign is a success or a failure. This is why understanding the true cost of Google Ads for a SaaS business is so important.

My Final Advice: The Vetting Checklist

Finding the right agency is a huge decision. To make it easier, I've boiled everything down to a final checklist. Before you sign any contract, make sure you can tick every one of these boxes.

I've detailed my main recommendations for you below:

Choosing an agency is a big commitment, and getting it wrong is costly. The difference between a generalist and a true SaaS specialist is the difference between burning cash and building a scalable, predictable engine for customer acquisition. A specialist won't just manage your ad account; they'll act as a strategic partner, helping you refine your offer, improve your funnel, and ultimately grow your business faster and more profitably.

Navigating this landscape, especially in a competitive hub like London, can be daunting. You're an expert in building software, not in the ever-changing world of paid advertising. Sometimes, the fastest way to get results is to work with someone who has already made the mistakes and learned the lessons on someone else's dime.

If you're tired of talking to agencies that don't get it and want to have a real conversation about growing your SaaS business with someone who understands the maths, consider booking a free, no-obligation strategy session with us. We'll take a look at what you're doing now and give you some actionable advice you can implement immediately, whether you decide to work with us or not.