Tony Blair will on Tuesday call a general election for May 5 as a new opinion poll for the Financial Times shows the Conservatives for the first time building a clear lead over Labour among Britons who say they are certain to vote.

As Labour braces itself for what is set to be its toughest election campaign since 1992, the poll by MORI shows the Tories have a five-point lead over Labour among people who say they will definitely vote in 30 days' time.