Details of the "personal issues" that forced shadow chancellor Alan Johnson to quit are starting to emerge amid allegations that the politician's bodyguard had an affair with his wife.

Mr Johnson's close protection officer when he was home secretary, Paul Rice, is facing an internal Scotland Yard inquiry over his alleged behaviour.

A decision is expected to be taken shortly on whether the constable will be suspended or relieved of duty while the probe takes place.

Mr Johnson quit as shadow chancellor on Thursday over what he described as "personal issues in my private life".

The officer is now protecting Home Secretary Theresa May.

Asked to comment on the report, a Scotland Yard spokesman said "certain matters regarding an MPS (Metropolitan Police Service) PC were referred to the directorate of professional standards. We are not in a position to discuss further at this time."

Mr Johnson's spokesman refused to comment on the claims, while the Home Office said it did not comment on personal security measures.

In his statement, Mr Johnson said only that it was "to do with my family. I have found it difficult to cope with these personal issues in my private life whilst carrying out an important front bench role," he added.

Mr Johnson has been married to his second wife Laura for almost 20 years and the couple have a ten-year-old son.

His resignation left Ed Miliband facing his biggest test since being elected Labour leader, forcing him to reshuffle his shadow cabinet less than four months into the job.

He installed Ed Balls as shadow chancellor after overlooking him last October.

Amid suggestions that Mr Balls may drag Labour to the left, Mr Miliband stressed that there would be no change in economic policy.

Mr Balls, a fierce ally of former prime minister Gordon Brown, has questioned Labour's deficit reduction plans in the past, suggesting they should be less aggressive.