Across the UK, marketers are facing a measurement gap with major business consequences. It’s estimated that one in five conversions are not being recorded because of browser restrictions, like the blocking of third-party tags. That means as much as 20% of campaign performance is invisible, which makes ROI appear weaker than it is, reduces the effectiveness of AI bidding, and erodes trust in marketing data at the leadership table.
This is not a future challenge; it is happening right now. “Browsers are actively blocking third-party tags, which means if you’re not adapting, you’re already missing valuable conversion data,” says Adam Taylor, data infrastructure lead at Google.
Across the digital advertising ecosystem, a fundamental shift is underway, driven by increasing user expectations for privacy. Major tech changes, such as tighter platform restrictions, are cutting off data points advertisers have long relied on to measure performance and understand customer journeys.
For brands, the most immediate hit is on measurement and reporting. “Brands are seeing gaps in their conversion data, which makes it difficult to accurately attribute sales or leads to the correct marketing channel,” says Luisa Del Maschio, senior analytics manager at Jellyfish.
“This data gap leads directly to media waste. When you can’t accurately measure what’s working, you can’t effectively optimize campaigns, meaning budgets are spent less efficiently and return on ad spend (ROAS) decreases. And that breeds something even harder to fix: strategic uncertainty.”
This isn’t just a technical degradation, Del Maschio explains, it’s a growing trust gap between what the data shows and what the business needs to move forward.
For years, the industry has reacted to privacy changes. Today, the shift is toward more proactive solutions that restore data responsibly while respecting user consent.
One option is Google Tag Gateway, which changes how Google’s measurement tags are delivered. Traditionally, tags from Google Ads, Google Marketing Platform, or Google Analytics were loaded from Google’s servers, making them third-party. Many browsers now block these by default.
“Google Tag Gateway allows those same tags to be served from the advertiser’s own domain,” explains Del Maschio. “That makes them first-party, so browsers don’t block them. The result is more complete conversion data, without changing how you measure success.”
This means marketers regain visibility into the customer journey, attribution becomes more accurate, and ROAS reflects reality.
“This enhanced data quality directly feeds into Google’s AI and automated bidding systems,” says Taylor. “Better data in means better optimization out, allowing Smart Bidding to make more effective decisions that drive better campaign results. Put simply, better data drives more effective bidding decisions, which can translate into stronger ROI and more efficient spend.”
At Jellyfish, clients implementing Google Tag Gateway have seen up to 11% more observed conversions in Google Ads and Analytics, with an average 15% uplift in ROAS. But beyond the percentages, Del Maschio says, the real win is confidence: “Decision-makers know their ROAS is accurate, making it easier to commit budgets and make bold, data-backed moves.”
Many CMOs worry this will be a heavy IT project. In reality, implementation is often straightforward. In some cases, setup can be completed in minutes without touching your site’s code; in others, a more tailored approach still has most advertisers live within a week.
The key is to approach this as a business initiative, not a technical upgrade. A simple checklist can help:
1. Identify your key stakeholders: Speak to your web development or IT team to find out if you use a Content Delivery Network (CDN) and who manages it. Use free online tools if you’re unsure - this will determine your easiest implementation path.
2. Know your numbers: Compare your customer database with your Google Analytics reports: how closely do they match? Some drop-off is normal with consent signals, but a bigger gap could mean you have a measurement problem worth fixing.
3. Check your tracking: A quick conversation with web development or IT about how your site’s tracking is set up can reveal whether a plug-and-play path to Google Tag Gateway is possible or if you’ll need a more tailored approach.
4. Measure the impact: Your goal as a marketer is improved performance - which should also mean you can invest more in marketing. Benchmark the results before and after to prove ROI improvements.
5. Educate yourself: Explore resources on first-party data and server-side solutions. Understanding the ‘why’ makes the ‘how’ much easier to tackle.
“Start with the numbers,” says Del Maschio. “Once the commercial impact is clear, the conversation shifts from ‘Do we have time for this?’ to ‘How quickly can we act?’”
For senior marketers, the message is clear: closing this data gap not only protects measurement, it also restores confidence, unlocks growth, and builds a stronger foundation for the privacy-first future.
As Del Maschio puts it: “Do this now and you can close a major data gap in days, not months.”
To learn more about Google Tag Gateway for advertisers, click here.
Google is committed to helping businesses thrive in a privacy-first world. The technology giant works with thousands of businesses and agencies to help them prepare...