Speaking to BBC Booktalk, the PM suggested making so many gaffes "nobody knows which one to concentrate on".
Liz Truss says she wants Boris Johnson to continue doing the job when asked if she had leadership ambitions.
By Alex Forsyth
Political correspondent, BBC News
The education secretary tells BBC Breakfast Nusrat Ghani's allegations must be investigated.
The culture secretary accused Tory MP William Wragg of "attention seeking behaviour" after his remarks.