By Jennifer Sieg Over half of London retailers are gearing up for a return to the high street in what is seen as a sign of positive momentum for the recovering retail sector, a new study has revealed. Some 55 per cent of London retailers have said they plan to open at least one new bricks and mortar store this year, according to a new American Express study shared exclusively with City A.M. The optimism comes during a time when renting costs and tough economic conditions have put a damper on the high street in recent years, with over 2,000 retailers going bust last year. Data from the ONS reve…