Last week Fitch downgraded the UK to AA+ owing to a weakened economic outlook.
This follows on from Moody's downgrade in February. The BBC quote Fitch as saying that the downgrade:
"Primarily reflects a weaker economic and fiscal outlook".However, it has placed the UK's outlook as being "stable"; ie it does not expect to downgrade the UK again in the foreseeable future.
As to whether austerity is the corset means of bringing about growth, only time will tell.