David Cameron’s most senior civil servant has been dragged into a row over political campaigning by ministerial aides.
Downing Street is said to have blocked attempts by allies of Home Secretary Theresa May to stand as MPs after they refused to canvass support for the Conservatives in the Rochester and Strood by-election last month.
Nick Timothy and Stephen Parkinson declined to take part, citing the code of conduct for special advisers, which states they would have to resign if they wanted to get involved.
The move to block their candidacy is seen as the latest power battle between No 10 and the Home Office amid claims Mrs May that is gearing up for a leadership bid.
Cabinet Secretary Sir Jeremy Heywood is reported to have agreed to an interpretation of the rules that allowed special advisers – known as “spads” – to campaign in their spare time in the Kent by-election.
Shadow Cabinet Office Minister Jon Ashworth has written to the Whitehall mandarin calling for him to publish the advice he issued about the rules advisers must abide by.
He also demanded to know what role the Prime Minister’s political private secretary Laurence Mann had in overseeing the campaigning activity of special advisers during the campaign.
Mr Ashworth said Sir Jeremy must also set out what discussions he and other civil servants within No 10 had with spads about campaigning during the by-election.
“The public will want clarity over whether highly-paid advisers...have been actively advised to breach important codes of conduct, which clearly ensure public funds are not used for political activity,” he wrote.