Labour backbencher Austin Mitchell called for an end to the bickering in the party, which he said was ‘‘like dogs fighting over a bone’’.
He said: ‘‘Here we have the people at the top of the tree tearing themselves apart over something which is comparatively unimportant.
‘‘There’s an obsession with gossip and trivia and who said what to whom and with handling the headlines.
‘‘This will get an appalling reaction in the party at large as well as in the House of Commons.’’
He said the public would be appalled by ‘‘the petty, argumentative nature of it all’’.
Mr Mitchell told BBC Radio 5 Live’s breakfast programme that those involved in the matter should ‘‘shut up’’ until the inquiry into the matter had been completed.
He said he felt a great deal of sympathy for Mr Mandelson on Wednesday when he announced his resignation but was bemused by his decision to speak out in Sunday papers.
‘‘It was an awful moment for him but when I see this whingeing self-defence in the Sunday Times I wonder what’s going on.’’
In the old days, he said, someone in Mr Mandelson’s predicament would have ‘‘retired to his room with a revolver and some whisky and shot himself’’.