SaaS User Acquisition: London Founder's Agency Guide

I get it. You're a SaaS founder in London, probably somewhere between Shoreditch and Canary Wharf, and you're drowning in a sea of "growth marketing agencies" all promising to skyrocket your user base. They've all got slick websites, talk a big game about AI-driven strategies, and probably have a WeWork membership. But when you dig a bit deeper, it all feels a bit hollow. You're right to be sceptical. Most of them are just B2C eCommerce agencies trying to slap the same old playbook onto the far more complex world of B2B SaaS, and it just doesn't work.

The truth is, finding a genuine user acquisition partner who gets the nuances of selling software in the UK market is incredibly difficult. It's not about finding someone who can just 'run ads'. It's about finding someone who understands the maths behind sustainable growth, the psychology of a B2B buyer, and how to turn a cold click into a long-term, profitable customer. Forget the hype. Let's talk about what actually works.

So, why is finding a decent agency in London so bloody hard?

The London tech scene is brilliant, but it's also incredibly noisy. Every other week there's a new agency popping up, fuelled by a bit of seed funding and a lot of confidence. The problem is that very few have genuine, repeatable experience with B2B SaaS. They might show you a case study for a fashion brand they got a 6x ROAS for, but that's a completely different universe to acquiring users for a complex software product with a long sales cycle.

They talk about 'brand awareness' campaigns, which is often code for "we'll spend your money showing your ads to people who will never, ever buy from you." For an early-stage SaaS, pure brand awareness is a luxury you can't afford. You need conversions. You need trials, demos, and paying customers. Awareness is a byproduct of a product that actually solves a problem, not a prerequisite for making a sale. You're paying Facebook or Google to find customers, not just eyeballs. Many agencies get this fundamentally wrong.

The other issue is transparency. You'll get pitched by a slick sales director, but the person actually managing your £10k, £20k, or £50k a month ad spend might be a junior account manager juggling ten other clients. You need to know who is actually in the trenches, optimising your campaigns day-to-day. You need direct access to the expert, not an account manager who acts as a go-between. This is a massive reason why we keep our client list small and focused. You talk to the person doing the work. For a complete breakdown of what to look for, our guide on vetting London paid ad agencies goes into much more detail on this.

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

This is where you can cut through 90% of the noise. Ignore the flashy logos and big revenue numbers without context. You need to look for evidence that they understand the specific unit economics of SaaS. Vague claims like "increased leads by 200%" are meaningless. What was the cost per lead? What was the quality of those leads? Did they convert to paying customers?

Here's what to look for instead:

-> Specific Cost Per Acquisition (CPA) Metrics: Look for things like "Cost per Trial," "Cost per Sign-up," or "Cost per Demo Booked." I remember one campaign where we achieved 5,082 software trials at a $7 cost per trial. That's a concrete, meaningful result. It tells you we understand how to acquire actual users, not just clicks.

-> Evidence of Optimisation and Scaling: A great case study doesn't just show a good result; it shows a journey. One of our proudest achievements was for a medical job matching SaaS. When we took them on, their Cost Per User Acquisition (CPA) was a painful £100. Through methodical testing of platforms, targeting, and creative, we reduced that down to just £7. That's not just running ads; that's transforming a company's growth potential. This is the kind of impact a true specialist can have.

-> Niche Relevance: Have they worked with B2B software before? It doesn't have to be your exact niche, but experience with SaaS, especially in the UK or other developed markets, is a huge plus. They'll understand the longer sales cycles, the importance of lead quality, and the different platforms that work. We've driven results for B2B software on LinkedIn, getting CPLs down to $22 for high-value decision makers, and on Meta, driving 4,622 registrations at just $2.38 each. This shows a versatility in finding the right channel for the right audience.

If an agency can't show you these kinds of results, with real numbers, they are not the right fit for your SaaS. It's that simple.

How do I even know what I can afford to spend?

This is the single most important question you need to answer before you even think about hiring an agency. So many founders focus on getting the lowest possible Cost Per Lead (CPL), without knowing what a good CPL for their business actually is. 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 your Lifetime Value (LTV).

If you don't know this number, you are flying blind. An agency could bring you leads at £50 a pop and you wouldn't know if that was a bargain or a disaster. Calculating it is simpler than you think.

You need three numbers:

1. Average Revenue Per Account (ARPA): What's your average monthly subscription price?

2. Gross Margin %: What's your profit margin on that revenue after server costs, support, etc.?

3. Monthly Churn Rate: What percentage of customers do you lose each month?

The formula is: LTV = (ARPA * Gross Margin %) / Monthly Churn Rate

Let's play with some numbers. Use the calculator below to see how your own metrics stack up. This isn't just a theoretical exercise; this is the core financial model for your growth. Understanding your B2B paid ads ROI starts right here.

Once you have this number, you can have an intelligent conversation with an agency. If your max CAC is £1,771 and your sales process converts 1 in 10 qualified trials into a customer, you know you can afford to pay up to £177 per trial. Suddenly, a £50 CPL from an agency doesn't just feel good, you *know* it's profitable. This is how you build a scalable acquisition machine.

What questions should I actually ask them on the discovery call?

The initial call is your chance to interview them, not the other way around. Their goal is to sell you. Your goal is to uncover the truth about their process and expertise. Don't let them just run through a generic slide deck. Take control and ask tough questions.

Here's a visual of what a proper vetting process should look like, from your initial search to making a final decision. Too many founders skip the deeper diligence steps.

Here are some questions to ask during that crucial discovery call:

1. "Walk me through the first 30 days of working with a new SaaS client like me."
A bad answer: "We'll do an audit, set up campaigns, and start driving traffic." (Too generic).
A good answer: "First, we'll deep-dive into your LTV and current conversion rates to establish baseline KPIs. Then we'll conduct customer interviews and competitor analysis to define the core 'nightmare' your product solves. We'll build initial campaigns on one primary channel, likely Google Search targeting high-intent keywords or LinkedIn targeting specific job titles, with a clear budget for testing creative and messaging. The first 30 days is about data collection and finding a signal, not scaling."

2. "Tell me about a SaaS campaign you ran that hit a plateau. What did you do to break through it?"
This question reveals their problem-solving skills. Everyone can launch a campaign; few can effectively optimise one that's stalled. Look for answers that involve methodical testing: expanding to new audiences (e.g., lookalikes of high-value customers), testing completely different creative angles (e.g., UGC video vs. static images), improving the landing page conversion rate, or even recommending changes to the offer itself (e.g., a free trial vs. a demo). A good partner thinks about the entire funnel, not just the ads.

3. "Who exactly will be working on my account? Can I speak with them?"
This is non-negotiable. You want to talk to the strategist or ad manager who will be in your account every day. If they're hesitant or want you to go through an account manager, it's a major red flag. This is a common issue with larger firms, and a good reason to consider a smaller, more specialised UK B2B ad agency where you get direct access to senior talent.

4. "What's your process for creative development and testing?"
For SaaS, the message is everything. You need to know how they translate your product's features into benefits that resonate with your ideal customer. Do they have a copywriter? How do they approach A/B testing? Do they have a structured process for it? They should talk about testing hooks, angles, visuals, and calls to action in a systematic way.

What does a good SaaS acquisition strategy even look like?

A competent agency won't just talk about 'running ads'. They'll talk about building a full-funnel acquisition system. In B2B SaaS, you can't just expect a cold user to see one ad and sign up for a £500/month plan. You need to build trust and demonstrate value over time.

This usually involves a structure like this:

-> Top of Funnel (ToFu): This is about getting in front of your Ideal Customer Profile (ICP) where they hang out online. For many B2B SaaS companies, this means LinkedIn Ads (targeting specific job titles, company sizes, and industries) or highly-specific Google Search campaigns. For instance, if you sell accounting software, a well-structured B2B SaaS Google Ads campaign targeting keywords like "small business accounting software uk" is a must. The goal here isn't necessarily an immediate sale, but to make them problem-aware and solution-aware.

-> Middle of Funnel (MoFu): Someone has visited your site or engaged with an ad but didn't convert. Now you retarget them. This is where you can show them different value propositions: a case study, a webinar, a different feature highlight. The goal is to nurture their interest and build trust. This is where a lot of the conversions will happen over time.

-> Bottom of Funnel (BoFu): They've shown strong intent—maybe they visited the pricing page or started to sign up but abandoned. This is where you hit them with a direct offer: "Start your free trial now," or "Book a 15-minute demo to see how we can solve [specific problem]."

The biggest mistake I see is companies (and agencies) spending all their budget on the bottom of the funnel, trying to get a quick conversion from a cold audience. It's expensive and it doesn't scale. A proper SaaS paid acquisition framework builds a pipeline of potential customers at all stages.

And for heaven's sake, delete the "Request a Demo" button as your main call to action for cold traffic. It's high-friction and low-value. A free trial (no card details required) or a genuinely useful asset (a checklist, a free tool, a report) will outperform it almost every time. You need to give value before you ask for their time. An agency that doesn't challenge you on your offer is just a media buyer, not a growth partner.

The Red Flags: When to run for the hills

As you go through this process, certain things should set off alarm bells. If you hear any of the following, it's probably best to walk away.

1. Guarantees and Promises: "We guarantee a 5x ROAS" or "We'll double your user base in 3 months." No one can guarantee results in paid advertising. There are too many variables. An expert will talk about a methodical process of testing and optimisation to *find* what works, not promise a specific outcome from day one.

2. Long-Term Contracts Upfront: A confident agency will be happy to start with a 3-month trial period. They know it will take time to get results, but they should be able to demonstrate progress and prove their value within that timeframe. Anyone pushing for a 12-month contract from the get-go is locking you in because they're afraid you'll leave.

3. Lack of Transparency on Fees: You should know exactly what you're paying for. Is it a flat retainer, a percentage of ad spend, or a performance-based fee? It should be crystal clear. Also be wary of agencies that blend their management fee into the ad spend; you should always have your own ad account that you own and pay for directly. For a guide on what to expect, check our breakdown of UK paid ads management costs.

4. They Don't Ask You Hard Questions: A great agency will grill you. They'll want to know your LTV, your churn rate, your sales cycle, your ideal customer's biggest pain point. If they just nod along and say "no problem, we can do it," they haven't understood the complexity of your business.

I've put together a summary table of my main recommendations. Think of it as a final checklist before you sign on the dotted line.

Choosing an agency is a big decision. It’s not just a vendor relationship; it's a partnership that can make or break your growth trajectory. The right partner will feel like an extension of your team, obsessing over your metrics and constantly finding new ways to grow. The wrong one will burn through your cash and leave you with nothing but a fancy report and a lot of frustration.

Doing this level of diligence takes time, but it will save you a fortune in the long run. If you want to see what this process looks like in practice and get an expert pair of eyes on your current situation, we offer a completely free, no-obligation strategy session. We'll audit your existing efforts (if any), analyse your business model, and give you a straightforward plan of action. Book a free consultation and we'll show you what a genuine growth partnership should look like.