Geordie Greig, the editor of the Mail on Sunday, has "unreservedly" apologised for sending a reporter to a memorial service for Ed Miliband's uncle.

Mr Miliband today attacked chairman Daily Mail and Mail on Sunday Lord Rothermere over the presence of a journalist the memorial service of his late Jewish uncle, Professor Harry Keen.

The Labour leader wrote a letter to Lord Rothermere which asked him to “reflect on the culture of your newspapers” after the uninvited reporter attended the memorial at Guy’s Hospital on Wednesday.

Professor Keen, who died aged 87 in April, was a renowned medical expert who was made a CBE for his services to the British Diabetic Association and to the NHS.

The reporter, who has not been identified, reportedly asked relatives for their response to the public row between Mr Miliband and the Daily Mail, after the newspaper ran a piece condemning the views of Mr Miliband’s late father, Ralph.

An outraged Mr Miliband said: "The editor of the Mail on Sunday has since confirmed to my office that a journalist from his newspaper did indeed attend the memorial uninvited with the intention of seeking information.

"My wider family, who are not in public life, feel understandably appalled and shocked that this can have happened.

"Sending a reporter to my late uncle's memorial crosses a line of common decency. I believe it a symptom of the culture and practices of both the Daily Mail and the Mail on Sunday.

"There are many decent people working at those newspapers and I know that many of them will be disgusted by this latest episode. But they will also recognise that what has happened to my family has happened to many others."

He added: "The reaction of many people to the Daily Mail's attacks on my father this week demonstrates that the way your newspapers have behaved does not reflect the real character of our country."