LONDON, June 30 (Reuters) - Britain said it wanted to help businesses to access state aid with a new and more flexible subsidy system, and that leaving the European Union would allow it to support domestic priorities like building green industry. The new system, which has previously been outlined by ministers, will be set out in legislation for the first time later on Wednesday. "When people ask "what are the benefits of Brexit?" - this is it," business minister Kwasi Kwarteng said on Twitter. He criticised the EU system, which previously applied to Britain until it completed its exit from the bloc at the end of 2020, as overly bureaucratic and slow. "The UK’s new, flexible system will empower public authorities to deliver subsidies to viable businesses in a timely and effective way," Kwarteng said. First outlined in February, the system will be based on the principle that subsidies are permitted if they deliver value for the British taxpayer. State aid would not be used to prop up ailing or insolvent firms indefinitely, or to allow one region of Britain to undercut another, the business department said. Britain has criticised states such as China for heavily subsidising state-owned enterprises that distort international trade. However, the government argues that its new plan will let it foster growth industries, small businesses and research and development.