Gavin Williamson was accused of withholding policy objections until a cabinet meeting so that they could be leaked

Senior Conservatives rounded on the defence secretary yesterday, accusing him of playing politics with the Northern Irish peace process to further his leadership ambitions.

No 10 expressed private irritation with Gavin Williamson after details of a cabinet row on Tuesday over plans to set up a historical murders unit in the Province were leaked to the press.

Mr Williamson objected to the plan, proposed by Karen Bradley, the Northern Ireland secretary, warning that it could lead to a “witch-hunt” against former members of the armed services.

But senior government sources said that Mr Williamson had signed off on the proposal before the meeting and accused him of ambushing Ms Bradley by leaving his objections until full cabinet so that they could be leaked.

“Last week