ARCH-BLAIRITE Andrew Adonis warned Jeremy Corbyn’s critics within Labour yesterday that it would be a “huge mistake” to form a breakaway party.

The peer, who led the Downing Street policy unit under Tony Blair, is not a natural ally of the left-wing Labour leader.

He caused considerable embarrassment for Mr Corbyn when he took a job as head of Chancellor George Osborne’s new National Infrastructure Commission.

But in his first interview since resigning the Labour whip to take the role, he insisted: “I saw it as doing something for the country. I’ve not given up my political views.”

And he advised trouble-making Labour MPs to set aside factional interests and remain part of a “broad coalition.”

He told House magazine: “Though at the present time there are sharply differing opinions inside the Labour Party over its future, to break up the party I think would simply hand power to the Conservatives for a generation.

“Not because the public would want the Conservative Party in power for generation, but simply because it wouldn’t have a clear choice.

“I think that’s a bad thing for democracy. It would be a huge mistake to break up.”

Mr Adonis warned that any breakaway would produce the same consequences as the SDP split in the 1980s — a split in the Labour vote that would be to the Tories’ advantage.

SDP founder David Owen, who left led a breakaway from Labour because of its leftward leap and opposition to EU membership, made a U-turn yesterday by backing a break with Brussels.

The former foreign secretary blamed the EU’s “inflammatory” language for starting the civil war in Ukraine.

“The EU-Ukraine agreement actually triggered this war, the wording in it was extraordinary,” he told the Today programme.