A leading international economic think-tank was warning that Britain is about to slip back into recession, it was reported Saturday.The Daily Telegraph newspaper said the Organisation for Economic Co-operation and Development (OECD) was forecasting that UK growth would be negative during the first half of 2012.The timing is highly sensitive for the Government with the OECD due top publish its latest forecasts on Monday, the day before Chancellor, Finance secretary, George Osborne delivers his autumn statement on the economy. The Telegraph, quoting government sources, said the Government was warned on Thursday that it would be predicting a new downturn in Britain because of the euro crisis. The paper said the OECD was forecasting the recession would be mild and that the economy would begin to recover during the summer.