Google Analytics 4 (GA4) is Google’s free analytics service for websites and apps: a tag on your site records what visitors do as a stream of events, and GA4 turns those events into reports on where people came from, what they looked at and whether they enquired or bought. It replaced Universal Analytics, which stopped processing data for standard accounts in July 2023.
How GA4 works
Everything in GA4 is an event. A page view is an event, and so is a scroll, a file download, a form start or a purchase. Each event carries parameters that add detail, such as the page address, a product name or an order value. Some events are collected as soon as the tag is installed, enhanced measurement adds more (outbound clicks and site search, for example) with a switch in the settings, and anything specific to your business, such as a quote request or a table booking, you define yourself.
The set-up has three layers. An account holds one or more properties; a property usually represents one website or business; and each property receives data through a data stream for the website or for an iOS or Android app. The web stream gives you a measurement ID starting with G-, which the tag uses to send data, whether it is pasted into the site or deployed through Google Tag Manager.
The events that matter commercially are marked as key events, which is Google’s current name for what GA4 used to call conversions. Standard reports give summaries, Explorations let you build funnels, paths and segments from the same data, and a free BigQuery export hands you every raw event when the interface runs out of detail.
Why it matters
For most UK small and medium businesses, GA4 is the one place where search, Google Ads, Meta Ads, email and direct visits are measured with the same ruler. Each ad platform reports its own results generously. GA4 at least applies one set of rules to all of them, which is what you need when deciding where the next pound of budget should go.
Other tools also read from it. Google Ads can import GA4 key events to steer automated bidding, most Looker Studio dashboards are built on it, and Search Console can be linked to it. That means a fault in GA4 spreads: a contact form counted twice becomes a Google Ads campaign optimising towards leads that never existed.
There is a legal layer too. GA4 sets cookies, so under PECR UK sites have generally needed the visitor’s consent before it runs, and the Information Commissioner’s Office expects refusing to be as easy as accepting. The Data (Use and Access) Act 2025 created an exemption for some analytics used purely for statistical purposes; at the time of writing (October 2026), check the ICO’s current guidance before assuming a standard GA4 set-up meets its conditions. A UK site running GA4 behind a proper banner will record fewer visitors than it really has, and that gap is expected rather than a fault.
Common mistakes
- Installing GA4 twice, once hard-coded in the theme and once through Tag Manager, so every page view and enquiry is counted double.
- Leaving data retention on the two-month default, which leaves year-on-year explorations empty.
- Marking too many events as key events. When scrolls and video plays sit beside sales, neither the reports nor the goals imported into Google Ads mean much.
- Counting a thank-you page view as a lead when the page can be reached by refreshing it or typing its address.
- Never excluding staff, agency and developer visits, so test enquiries inflate the lead count.
- Loading GA4 before the visitor has answered the cookie banner.
- Comparing GA4 user and session counts with old Universal Analytics figures as though both measured the same thing. They count differently.
How to act on it
Start with an inventory. In Admin, confirm there is one property for the business and one web data stream, and that its measurement ID matches the one actually firing on your pages, which Tag Assistant or your browser’s developer tools will show. Then check the settings that quietly decide data quality: data retention set to 14 months, internal and developer traffic filters, unwanted referrals such as payment providers, and the links to Google Ads and Search Console.
Next, write down the three to five actions that genuinely matter to the business, such as an enquiry form, a click on the phone number, a booking or a purchase, and make those the key events. Complete each one yourself and confirm it appears once, with the right value, in DebugView and then in the reports the following day.
Finally, test consent. In a private window, load the site, reject cookies and confirm GA4 behaves as your set-up intends; then accept and confirm the data flows. A set-up tested this way is the foundation for performance marketing judged on real enquiries and sales, which is the work I do for UK businesses.