Media playback is unsupported on your device
Theresa May is continuing to face pressure from her own MPs to resign after one of her senior ministers quit the cabinet.
The Leader of the House, Andrea Leadsom, stepped down on Wednesday night over the PM’s Brexit policy.
Several cabinet ministers have also told the BBC that the PM cannot stay in her post.
Mrs May said she was “sorry to lose someone of [Mrs Leadsom’s] passion, drive and sincerity”.
Speaking to reporters on Wednesday night, Mrs Leadsom said Mrs May’s new Brexit plan had “elements I cannot support, that aren’t Brexit”.
The minister had been due to appear in the Commons on Thursday to give a business statement to MPs.
Mrs Leadsom was set to announce when the prime minister’s Withdrawal Agreement Bill – the legislation needed to implement the agreement between the UK and EU on the terms of Brexit – would be introduced to Parliament.
However, it is now not clear who will take her place at the dispatch box.