Cookie Controls, Signal Loss and First-Party Data: A Positive Shift for UK Marketers

In 2025, the digital advertising landscape has undergone the most significant shift since programmatic began. Third-party cookies are weakening, browsers are imposing stricter privacy rules, and users increasingly expect transparency.

While Google’s recent decision not to enforce a full cookie phase-out has added confusion, the direction of online advertising is the sam. cookie-based advertising is steadily eroding. But this does create an opportunity for smarter planning and stronger first-party data strategies.

Where Google Now Stands

In 2025, in the UK, we have seen the Information Commissioner’s Office (ICO) crackdown and compliance enforcement plus the Data (Use and Access) Act get Royal Assent, but Google has been the focus for many in 2025. Outside of the search engine, it has Chrome, which has around 2/3 of the browser market share, plus they dominate the ad-server market and the ad-exchange market. So whatever Google do will have a massive impact on global advertising.

Google originally planned a hard shut-off of third-party cookies in Chrome. After regulatory pressure, industry resistance and practical concerns, Google stepped back from a universal “switch-off”. Instead:

• Chrome will give users the option to disable cross-site cookies.
• Privacy Sandbox tools will continue, but adoption is voluntary.
• Third-party cookies remain, but in a more restricted, less reliable form.

For UK marketers, the implication is:

Cookies won’t disappear overnight — but they no longer provide dependable reach or reporting. Planning as if they are stable is a risk.

Safari and Firefox already block them by default, iOS restricts cross-site tracking, and opt-out rates across Europe are high. The cookie may be lingering, but it is no longer a foundation to build a strategy on.

What Changes for Advertising, Tracking and Measurement?

Even without a hard deprecation, several established practices continue to weaken:

Audience Targeting

Retargeting and behavioural prospecting on the open web are less reliable because fewer users can be identified consistently. Cookie match rates are dropping year-on-year.

Attribution and Reporting

Cross-site user journeys are harder to observe, and traditional view-through and multi-touch attribution models lose accuracy. More conversions fall into “untracked” or “modelled”. This is why, at Altair, we are leaning into machine learning and AI to open up Mixed Media Modelling (MMM) for our clients.

Media Planning

Over-reliance on cookie-enabled programmatic buying has created blind spots. Large portions of UK audiences (especially on Safari and iOS) have already been untrackable for years.

The positive side is that this transition forces marketers to clean up their data foundations, reassess channel value, and rebalance budgets based on real, reliable signals rather than old school habits.

First-Party Data Becomes the Strategic Centrepiece

The biggest upside of cookie decline, which we have been saying for so many years now, is the renewed focus on first-party data. Data collected directly and consensually from customers via logins, purchases, site interactions or subscriptions.

It's important to view first-party data as your most valued asset. It needs to feed, grouped nicely and cleaned on an on-going basis.

Strong first-party data enables:

• More accurate audience understanding
• Better personalisation
• Durable targeting across multiple channels
• Improved retention and lifetime value strategies

This is the basis of deterministic targeting: where user identity is known and verified, typically via a login or hashed email. It is incredibly accurate but only applies to audiences with whom a brand has a direct relationship.

For broader reach, marketers complement it with probabilistic approaches. These are cohort targeting, contextual intelligence, predictive modelling, which infer intent or group membership without identifying individuals.

The future is not deterministic or probabilistic. It’s the smart combination of both.

How Server-Side Measurement and Conversion APIs Fit In

One of the most important adaptations in a reduced-cookie environment is shifting conversion tracking away from the browser.

Why browser tracking is failing

Pixels and client-side tags rely on:

• Cookies
• JavaScript
• Browsers allowing cross-site communication

When a browser blocks any of those, the conversion is lost, meaning Meta, Google, TikTok or LinkedIn receive incomplete signals.

The modern approach: conversion APIs & server-side tagging

Platforms now encourage advertisers to send conversion events directly from their server to the ad platform.

Examples include:

• Meta Conversion API
• Google Enhanced Conversions & server-side GTM
• TikTok Events API
• LinkedIn CAPI

This approach:

• Recovers conversions lost to browser blocking
• Improves bidding efficiency
• Supports privacy-safe attribution
• Future-proofs measurement as client-side signals decline

In practical terms, it keeps campaigns optimising effectively even when browser-based tracking breaks.

Channel-by-Channel Impact

Programmatic Display

This is the most affected area. Cookie-driven audience buying weakens, so contextual targeting, publisher first-party data, and ID-less solutions gain importance. Modern contextual tools are far more accurate than a decade ago, making this shift more positive than many expect.

Social Platforms

Social ecosystems remain strong because they operate on deterministic, logged-in data. However, iOS restrictions reduced their visibility into off-platform behaviour, making server-side integrations essential for accurate optimisation.

Search

Search targeting itself remains intact, it’s based on keywords not identity. The main shift is in measurement, where modelled conversions and enhanced server-side data now fill gaps left by browser restrictions.

The UK Position: Ahead, But Still Preparing

The UK’s GDPR maturity means marketers here adapted earlier than many other countries. Safari and iOS already created a semi-cookieless reality, so UK teams have experience working with reduced signals.

However, readiness varies. Some paused preparation when Google delayed deprecation, but the industry shift continues regardless. 2025 was a key year for reinforcing data foundations, consent strategy, server-side measurement and first-party data refinement.

A Chance to Build Better Marketing

This transition is not a setback. It encourages:

• Cleaner, more trusted data
• Less waste and duplication
• Better customer relationships
• Stronger strategic thinking
• Increased emphasis on creative and contextual quality

The most effective marketers will be those who see this shift not as the death of an old tool, but as the birth of a more resilient and user based advertising model.