Image copyright EPA Image caption The Tory candidate, Kelly Tolhurst, was defeated by UKIP in the Rochester and Strood by-election

The Conservatives have suspended two of Theresa May's aides from a list of 2015 general election candidates amid a row.

Nick Timothy and Stephen Parkinson were suspended from the party's candidates list on the grounds that they did not campaign in the Rochester by-election.

But they said they had believed campaigning would have breached the special advisers' code of conduct.

A Tory source denied claims their suspension showed tension between the home secretary and Downing Street.

The source added that Mrs May's aides were among several potential candidates suspended from the parliamentary candidates list for next May's general election for not campaigning and other cases were being considered.

The rift was made public in an exchange of letters published by the ConservativeHome website.

Mr Timothy, the home secretary's chief of staff, was on the candidates list for the West Midlands seat of Aldridge Brownhills.

It is understood that Conservative Party officials wrongly told the constituency association that he had withdrawn from the list. In fact. he had been suspended on the grounds that he "did not participate in telephone canvassing during the Rochester by-election campaign".

'Disproportionate'

Mr Timothy wrote to the chair of the association insisting that he had not withdrawn from the selection voluntarily and challenging the grounds for his suspension.

He had not taken part in canvassing, he wrote, because he believed himself bound by the code of conduct preventing special advisers from direct political campaigning.

According to ConservativeHome, he added: "Even if the reason to suspend me from the list was valid, it would have been entirely disproportionate, because I have devoted most of my adult life to the Conservative Party, as a volunteer and officer and as a professional. I have been a branch chairman and a local council candidate, and I have canvassed in more election campaigns than I can remember."

Last month's by-election in Rochester and Strood was triggered by Tory MP Mark Reckless's defection to UKIP.

The Conservatives mounted a large-scale campaign with senior figures including David Cameron and William Hague visiting the Kent constituency and ministers and MPs under orders to visit the constituency more than once.

Special advisers were told to take part and reassured they were allowed to volunteer for telephone canvassing under civil service rules.

Code of conduct

But a Whitehall source told the BBC that many advisers were concerned, fearing opponents would use any campaigning as an opportunity to make a formal complaint and try to force them from their jobs.

The code of conduct says special advisers who want to take part in election campaigns must first resign.

In a statement, a Cabinet Office spokesman said "back office" campaign work would not breach the special advisers code.

The spokesman said: "Special advisers have always been able in their own time and outside of office hours to take part in back office activities. This is not inconsistent with the code. "

The row comes after Theresa May's special adviser Fiona Cunningham stood down in June after she was found by a Downing Street inquiry to have been the source of a negative briefing against the then Education Secretary Michael Gove.