The 'Mail on Sunday' has "unreservedly" apologised to Ed Miliband after an uninvited reporter went to a private memorial service he was attending for his late uncle.
The paper's editor Geordie Greig promised a full investigation after the Labour leader complained that the reporter attempted to get reaction from his relatives about an article in its sister paper, the 'Daily Mail', denouncing his late father, Marxist intellectual Ralph Miliband, as the man "who hated Britain".
Mr Greig said it had been a "terrible lapse of judgment" and two journalists on the paper have been suspended.
"I unreservedly apologise for a reporter intruding into a private memorial service for a relative of Ed Miliband," he said.
"The reporter was sent without my knowledge; it was a decision which was wrong. Two journalists have been suspended and a full investigation is now being carried out.
"I would further like to apologise to members of the family and friends attending the service for this deplorable intrusion. I have already spoken personally to Ed Miliband and expressed my regret that such a terrible lapse of judgment should have taken place."
Following the incident Mr Miliband has called on the proprietors to mount an urgent inquiry into the papers' "culture and practices".
In a letter to Lord Rothermere, the chairman of Daily Mail and General Trust, he said the decision to send a reporter to the memorial service held yesterday at Guy's Hospital for Professor Harry Keen crossed "a line of common decency".