Former Liberal Democrats leader Paddy Ashdown has claimed key Labour party figures have signalled they would defect to the Liberal Democrats if the party becomes too left wing.

In an interview with the Daily Telegraph, Lord Ashdown told the paper that Labour MPs were concerned by the party’s shift towards the left in the wake of the announcement of the 50 per cent top rate of income tax.

He added that there was already concern about the mood in constituencies and that an election loss could prove to be the final straw for some senior party members.

Mr Ashdown said: “What happens if Labour loses? Very senior people have told me there will be a heart and soul battle.

“If there is a real fight, the ingredients will be ripe for a repeat of what happened prior to 1983. There are signs that certain constituency parties are growing really Left-wing, such as in Leeds. Senior Labour figures have said to me ‘if that happens, I’m off’.”

In 1981, four Labour party members defected to form the SDP. The Labour party lost the following general elections in 1983 with Margaret Thatcher becoming prime minister.

The past week has been difficult for the government with Gordon Brown suffering a shock Commons defeat over the settlement rights of Gurkhas and him withdrawing plans to reform MPs expenses.