The Standard & Poor's credit rating agency's revision of the UK's outlook from stable to negative is the third such blow for the British economy this year:
- Moody's rating agency placed the UK on negative outlook in February
- In March, the Fitch agency followed suit, dropping the UK's outlook from stable
- S&P today completed the trio of agencies warning that the UK's coveted AAA rating is in danger
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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.