LONDON (AP) -- The Standard & Poor's rating agency has put Britain's AAA long-term credit rating on negative watch because of fears that economic growth over the next two years could be weaker than forecast.

S&P said Thursday that it believed that many of the factors that have held back UK economic growth will persist. The agency added, "we continue to believe the government's efforts over the next few years to engineer the planned correction in the U.K.'s fiscal accounts will likely drag on economic growth."

The negative outlook reflects the agency's belief that there is a 1-in-3 chance that the rating will be lowered within two years.

Fitch placed Britain's rating on negative outlook in March, and will conduct a review next year, while Moody's (MCO -0.09%) announced a negative watch in February.