Mr McDonnell said he had once been asked in a warm-up question on the BBC’s Any Questions what he would do if he found himself in an Ashes To Ashes situation – a reference to the time-travelling TV series where a policewoman finds herself transported back to the 1980s.

To applause from the audience in Southport, Merseyside, he said that he would have liked to go back to that era and ‘assassinate Thatcher’.

The MP for Hayes and Harlington in West London – who served as Ken Livingstone’s deputy at the Greater London Council – insisted his comments were ‘a joke and it went down as a joke’.