Alan Johnson's ex-bodyguard has been suspended over allegations that he had an affair with the former shadow chancellor's wife.
The episode led Mr Johnson to quit Labour's frontbench on Thursday night.
Close protection officer Pc Paul Rice guarded Mr Johnson when he was home secretary. He is thought to have worked for Theresa May since she took over at the Home Office last May.
Mr Johnson has refused to elaborate on the "personal reasons" for his shock resignation, saying only that he was finding it "difficult to cope" with "personal issues in my private life".
He has been married to Laura, his second wife, for almost 20 years. The couple have a ten-year-old son.
His resignation left Mr 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.