Google Consent Mode v2: A Plain-English Guide for UK Businesses

If you run Google Ads or GA4 for a UK audience, consent mode v2 is no longer optional background plumbing. It decides what Google can measure when visitors accept or reject cookies, and whether your remarketing lists and conversion data keep working. This guide explains it in plain English, without the legal fog.

Quick answer: Google Consent Mode v2 is a framework that passes each visitor's cookie choices to Google tags. It uses four signals: `analytics_storage`, `ad_storage`, `ad_user_data` and `ad_personalization`. Tags then adjust their behaviour. In basic mode, Google tags do not load until consent is given. In advanced mode, they load straight away and send cookieless pings when consent is denied, which lets Google model some of the missing conversions.

What is Google Consent Mode?

Google Consent Mode is not a cookie banner. It is a layer that sits between your consent management platform (CMP), the tool that shows the banner, and your Google tags (GA4, Google Ads, Floodlight).

Your CMP records what the visitor chose. Consent mode translates that choice into signals Google tags understand. Without it, your banner may block tags crudely, or worse, not block them at all.

What changed in consent mode v2?

The original version used two main signals. Version 2 added two more, driven by the EU Digital Markets Act and Google's updated EU user consent policy. From March 2024, Google began requiring these signals for traffic from the European Economic Area and the UK if advertisers want to keep using features such as remarketing audiences and personalised advertising.

The four signals are:

• analytics_storage: whether cookies can be used for analytics, such as GA4.
• ad_storage: whether cookies can be used for advertising, such as Google Ads conversion cookies.
• ad_user_data: whether user data can be sent to Google for advertising purposes.
• ad_personalization: whether data can be used for personalised advertising, such as remarketing.

If `ad_user_data` and `ad_personalization` are missing or denied, expect audience building and some measurement features in Google Ads to be restricted for those users.

Basic vs advanced consent mode

This is the decision that matters most, and it is often made by accident.

Basic consent mode

• Google tags are blocked until the visitor interacts with the banner.
• If they accept, tags fire normally with the right consent state.
• If they reject, nothing is sent to Google at all.
• Google Ads can still apply a general conversion model, but it is less precise because it has no signals from non-consenting users.

Advanced consent mode

• Google tags load as soon as the page loads, with default consent set to denied.
• If the visitor rejects, tags send cookieless pings: no cookies are read or written, but basic, non-identifying signals such as the fact that a conversion happened are sent.
• Google uses these pings to model the behaviour and conversions of non-consenting users.
• In GA4, behavioural modelling can fill some of the gaps, but only when the property meets Google's eligibility thresholds for traffic and consented data.

Which should you choose?

Advanced mode usually recovers more measurement, so it is popular with advertisers. However, it sends some data before consent, so the decision should involve whoever owns privacy compliance in your business. Under UK rules (PECR and UK GDPR, enforced by the ICO), storing or reading non-essential cookies needs consent. Advanced mode is designed not to set cookies without consent, but you should be comfortable with the data it does send and describe it accurately in your privacy notice.

What matters is that you choose deliberately and set it up consistently. A half-configured setup is worse than either option.

How to set up consent mode v2 in GTM

Most UK sites implement consent mode v2 through Google Tag Manager, usually with a Google-certified CMP such as Cookiebot, CookieYes, OneTrust, Usercentrics or Termly. Many CMPs offer a GTM template that handles most of the work.

A typical consent mode v2 GTM setup looks like this:

1. Pick a certified CMP. Google maintains a list of CMP partners that support consent mode v2. Using one saves a lot of custom code.
2. Add the CMP template in GTM. Install it from the Community Template Gallery and fire it on the Consent Initialization - All Pages trigger, so defaults are set before anything else runs.
3. Set default consent states. For UK and EEA visitors, all four signals should default to `denied`. Some CMPs let you use region-specific defaults.
4. Confirm updates fire. When a visitor makes a choice, the CMP should push a consent `update` with the new values.
5. Review tag consent settings. In GTM, enable the consent overview (Admin, Container Settings, Enable consent overview). Google tags have built-in consent checks. Non-Google tags, such as Meta or LinkedIn, need "additional consent required" settings so they only fire when the relevant consent is granted.
6. Decide basic or advanced. For basic mode, block Google tags until consent. For advanced, let them load and rely on built-in consent checks.
7. Publish and test. Do not assume it works because the banner appears.

If you hard-code the Google tag (gtag.js) instead, the same principle applies: a `gtag('consent', 'default', {...})` call must run before the Google tag config, followed by `gtag('consent', 'update', {...})` when the visitor chooses.

How to check consent mode v2 is working

This is where most implementations quietly fail. Here is how we test it.

Use Tag Assistant

Open your site in Google Tag Assistant preview mode. On the Consent tab, check:

• The default state shows all four signals as denied before any interaction.
• After accepting, an update event shows them as granted.
• After rejecting, they stay denied.

Check network requests

In your browser's developer tools, filter network requests for `collect` (GA4) or Google Ads conversion calls. Look for the `gcs` parameter (for example `G100` means ad and analytics storage denied, `G111` means both granted) and the `gcd` parameter, which encodes all four signals. In advanced mode you should see pings even when consent is denied, but without cookies being set.

Check Google Ads diagnostics

Google Ads shows consent mode status on conversion actions, and GA4 shows a consent settings panel under Admin, Data collection and modification, Data streams. Use these as a sense check, not a substitute for testing.

Common consent mode v2 mistakes

• Defaults set too late. If the consent default fires after the Google tag, the first hit may be sent without consent information.
• Only two signals configured. Older setups often send `ad_storage` and `analytics_storage` but not the v2 signals.
• Banner blocks tags and consent mode at once. Some setups block Google tags entirely and also try to run advanced mode, which defeats the point.
• Non-Google tags ignored. Consent mode only governs Google tags. Meta, TikTok and LinkedIn tags still need their own consent conditions.
• Defaults set to granted for UK visitors. This is a compliance risk and is easy to miss.
• Nobody re-tests after changes. A theme update, new CMP version or GTM edit can break the flow without any visible error.

What consent mode v2 means for your reporting

Even when correctly set up, consent mode v2 does not give you back every lost user. Expect:

• Fewer observed users and sessions in GA4 than in server logs or your CRM.
• Modelled conversions in Google Ads that can shift slightly as modelling updates.
• Gaps between platforms, which we cover in how cookie banners affect your analytics.

Consent mode works best alongside first-party data measures such as enhanced conversions for Google Ads, which improve matching for users who have consented.

Is consent mode v2 a legal requirement?

Consent mode itself is a Google technical requirement for certain features, not a law. The law, in the UK, is PECR and UK GDPR, which require valid consent for non-essential cookies. Consent mode is how you respect that consent in Google's tools while keeping as much measurement as is legitimately possible. If you are unsure about your legal position, take advice from a privacy professional.

FAQs

Do I need consent mode v2 if I only use GA4?

It is strongly recommended. GA4 behavioural modelling and correct handling of consent depend on it, and if you link GA4 to Google Ads, the advertising signals matter too.

Will consent mode v2 recover all my lost data?

No. Advanced mode enables modelling, which estimates some missing conversions and behaviour. It does not recreate individual user journeys for people who declined.

Can I set up consent mode v2 without a CMP?

Technically yes, with custom code, but it is harder to maintain and easier to get wrong. A certified CMP with a GTM template is the more reliable route for most businesses.

How do I know if mine is set up correctly?

Test it in Tag Assistant and check the `gcs` and `gcd` parameters on network requests before and after accepting and rejecting cookies.

Get your consent setup checked

If you are not sure whether your banner, consent mode and tags actually work together, our Tracking Audit + Fix (£199) tests your consent mode v2 setup, GTM configuration and conversion events, and fixes what is broken. Fixed fee, no retainer. Get My Audit.