Fitch Ratings has downgraded the UK from AAA to AA+, but said that the outlook is stable.
The rating actions follow the conclusion of the review of the UK's sovereign ratings initiated on 22 March.
Fitch has explained that the reason for the downgrade is that despite the UK's "strong fiscal financing flexibility", its ability to absorb further adverse economic shocks is "no longer consistent with an 'AAA' rating".
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