Conservative leader David Cameron has personally entered into the election battle for Croydon Central by urging constituents not to vote for Andrew Pelling.

Mr Cameron has written a personal letter to residents in Croydon Central after Mr Pelling decided to stand as an independent candidate It comes as local Conservatives issued seven pages of anti-Pelling briefing notes highlighting Mr Pelling’s previous mental health problems.

A document from the Croydon Central and South Conservatives Federation urges party members to support its candidate Gavin Barwell.

It refers to Mr Pelling’s depression and his marital problems and includes examples of him “attacking” the council, former friend Mr Barwell and Mr Cameron.

The document read: “Following some very unpleasant media coverage, Andrew suffered a second bout of depression he had initially experienced when his first wife Sanae left him in late 2004.”

The briefing was released after Mr Pelling announced his decision to stand as an independent candidate.

The three main political parties recently agreed a protocol to stop politicians using opponents’ mental health problems to win political advantage. It was drawn up by mental health charity Mind and other organisations.

Mind’s chief executive Paul Farmer said: “We want to see an election where mental health is not used negatively in campaigning.

"The election compact on mental health effectively bans politicians from making slurs about opponents’ mental health and we encourage all candidates to adhere to the terms of this agreement.”

Mr Pelling said: “I am surprised about the highlighting of my mental ill-health.

“David Cameron had joined Gordon Brown and Nick Clegg in signing the compact abjuring references to mental ill-health of candidates in the election undertaking ‘not to stigmatise, slur or discriminate’ so the Conservatives have gone back on that signed undertaking pretty quickly.”

Pat Putwyn, 77, a member of the Conservative Party who received the letter from David Cameron, said: “I was extremely upset about it as a member of the party.

“I was very disappointed. I feel sorry for Andrew because I think some things have been said that are not correct.”

Unlike the briefing document, Mr Cameron’s letter does not refer directly to the Croydon Central MP’s depression.

But it does mention that Mr Pelling was arrested in September 2007 after “serious allegations” made by his ex-wife Lucy.

Terry Grourk, chairman of the Croydon Central and South Conservative Federation said: “I wanted to give our members the full background to all the facts.

"The letter was only sent personally to our members in Croydon Central constituency and was not intended for any wider circulation.

“I am fully aware of the All Party Group on Mental Health Compact which promises that, during the campaign, no party should make slurs on any candidate’s mental health, or stigmatise, slur or discriminate anyone with a mental health problem.

“The Conservative party locally has not broken this compact and I have only referred to a situation that is already in the public domain, as reported by the Croydon Guardian on January 4, 2008.”