Ken Livingstone criticised by Labour peer Robert Winston
24 April 2012 Last updated at 13:57 BST
Lord Winston said the party's candidate for mayor of London was "quite a tricky sort of customer" who has "espoused some disastrous causes".
The Labour peer said the party should have had a "fresher view" for the capital than Ken Livingstone.
Seven candidates are on the 3 May ballot papers.