Yes the UK credit rating is down, and it seems to be harming not only the UK. Sadly markets went down without a plan in place to protect the rating. Fitch Rating has already come out and spoken about the downgrade of the Long-Term Foreign and Local Currency Issuer Default Ratings.
A credit rating company recently gave the UK's credit a dismally low score. This is the first of many problems that the UK will face following their decision to leave the EU: given that their credit ratings are so low, it's only a matter of time before they dive even further after they get no financial support from their EU friends.
You only have to look at the falls in the pound and on the likes of the FTSE 250 in recent days to see the concern among traders. The point is, Britain should always be able to pay its debts, which makes bonds safe, but that doesn't mean the economy will emerge unscathed.
The UK has lost its top credit rating following the Brexit vote. It has said that the referendum result could lead to a deterioration of the country's economic performance, including its large financial services sector. Other financial agency's have forecasted an abrupt slowdown in growth in the short-term. This all comes after Chancellor George Osborne said that the UK will face the future from a position of strength.