Britain will back a modular nuclear power station for Anglesey Island in northern Wales, ending years of uncertainty over the fate of what is considered the country’s best nuclear site. The decision, which was announced Thursday morning in London, appears to be an effort to create a British nuclear champion and a move to increase the government’s role in the economy, especially the energy sector. The Wales plant would also be the first of this type of nuclear plant to be built in Britain. Modular designs are promoted as cheaper and quicker to construct. Rolls-Royce SMR, an affiliate of the jet engine maker that is one of Britain’s few remaining large industrial companies, will design the power station at Wylfa, a rocky headland on the island that overlooks the Irish Sea.