STOCKHOLM (Reuters) - Fortnite maker Epic Games said on Tuesday it had filed a complaint with Britain’s competition regulator in support of its investigation into Apple Inc’s anti-competitive behaviour. The UK Competition and Markets Authority said earlier here this month it had opened an investigation into Apple after complaints that the iPhone maker"s terms and conditions for app developers were unfair. Payment policies related to Apple’s App Store have long drawn complaints from app developers as they requires them to use its payment system, which charges commission of between 15% and 30%. Epic and Apple have engaged in multiple lawsuits across the world since the dispute over app payment commissions surfaced last year. Apple barred Epic’s Fortnite from the App Store after the game-maker tried to avoid Apple’s 30% fee on some in-app purchases on the App Store by launching its own in-app payment system. Epic Games founder and Chief Executive Tim Sweeney, a vocal critic of Apple’s policies, said its “practices lead to artificially inflated costs for consumers, and stifle innovation among developers”. “It is not surprising that Epic is pushing their agenda before the UK Competition and Markets Authority, as we have seen them use the same playbook around the world,” an Apple spokesman said. The gaming company has ongoing lawsuits against Apple in Australia and the United States, and filed an antitrust complaint in the European Union. Epic wants to operate under a different set of rules than the ones that apply to all other developers... We think that’s wrong, Apple said.