The Syrian information minister has denied that Bashar al-Assad's motorcade in Damascus was hit by rebels, Reuters reports.
More top news
The chancellor now faces the prospect of forming a minority government or calling for a snap election.
The 73-year-old said a return is unlikely "given the politicised atmosphere that seems to have afflicted our set."
Chancellor Philip Hammond said the UK will make a financial proposal to the EU in the next three-and-a-half weeks.