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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Images of the Duke and Duchess of Cambridge, with Kate cradling the young prince in her arms, feature on nearly all the front pages.
A family spokesman said the 93-year-old is “responding to treatments and appears to be recovering”.
The prince of Cambridge arrived on Monday, weighing 8lb 7oz.