Credit ratings agency Moody's has downgraded the UK Government's bond rating from stable to negative in light of Britain's decision to leave the European Union.
The agency warns Britain's economic growth will be weaker, its economic policymaking may be diminished and the government's fiscal strength reduced.
Moody's said: "Moody's expects a negative impact on the economy unless the UK government manages to negotiate a trade deal that largely replicates its current access to the Single Market.
"However, at the moment there is substantial uncertainty over the type of trade agreement that could be achieved."
The agency also affirmed Britian would remain on the AA+ rating, three years after it cut Britain's AAA rating.
Some have suggested financial markets have been engulphed by a "Black Friday" as traders around the world resonded to the consequences of Britain's exit from the EU.
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