A survey of 20 economists by the FT finds that Sterling's high exchange rate may be less of a barrier to membership of the European single currency than previously thought. The average suggested entry rate was £0.68 to the euro, just 8.5 per cent below current levels.

However, a study by PriceWaterhouse Coopers also released yesterday suggested that the UK and European economies were in fact diverging, reducing the chances of Britain joining the euro.

Britain risks "slow economic decline" outside the euro, a group of seven business leaders warns today in a letter to the Times.