A legal action seeking damages of up to £920m from Google on behalf of 19.5 million UK Android phone users has been launched.
It claims the 30% cut Google takes from digital purchases on its app store is excessive and unfair.
The case follows a similar one launched on behalf of iPhone users in May.
Google said it competed "vigorously and fairly" for developers and consumers and its fees were "comparable to our competitors".
Most Android phones came pre-loaded with more than one app store.
And 97% of developers paid no service fee because their apps were free.
"This lawsuit ignores the benefits and choice Android and Google Play provide as well as the competitive market in which we operate," it said.
Google recently cut its service charge to 15% for all developers earning less than £1m, with only a tiny fraction of the most profitable app developers paying 30%.
The charge "allows us to constantly reinvest in building a secure, thriving platform that benefits everyone who uses it", it added.
But both Apple and Google's charges have come under intense public scrutiny, following a massive row with Epic Games and subsequent legal action.
Epic argued the Play Store and Apple's app store were monopolistic and is seeking the ability to place Fortnite on both, with an independent payment-processing system.
This UK legal action alleges:
- Google broke European and UK competition laws with the 30% surcharge and as a result is overcharging millions of app users who make purchases via the Play Store.
- because Google bundles the Play Store with other products and requires pre-installation of it, consumers have little alternative but to pay the charges set out by Google
The claim has been filed with the Competition Appeal Tribunal (CAT), by former Citizens Advice consumer-policy lead Liz Coll.
The CAT has allowed "collective actions" - similar to US-style class-action cases - subject to initial approval, since 2015.
They differ from normal legal cases in that all affected people are automatically covered unless they decide to exclude themselves.
Ms Coll said: "Google created the Android app marketplace and controls it with a vice-like grip.
"Customers are herded towards the Google Play Store and, once there, have no option but to pay a 30% fee whenever they buy an app or make an in-app purchase.
"Competing app stores, which could give the same service at a fraction of the price, never get a look in."