By William Schomberg LONDON (Reuters) -The risk of a two-year recession in Britain, flagged this week by the Bank of England, underscores the high stakes for Prime Minister Rishi Sunak and his finance minister Jeremy Hunt as they prepare to announce major tax increases and spending cuts. The BoE said on Thursday that Britain’s economy would shrink for eight three-month quarters in a row – the longest such run in at least a century – if interest rates go up by as much as financial markets have been expecting recently. That would be a longer and shallower economic contraction than the ones that …