LONDON—Fitch Ratings Inc. has affirmed its A+ rating on the Lloyd’s of London market but said 2010 likely will be a more challenging year for the market than 2009.

Fitch said the rating affirmation reflected Lloyd’s strong operating performance in 2009, which exceeded the agency’s expectations.

But Fitch said the market’s 2009 results were boosted by a series of factors that are unlikely to be repeated in 2010, including a benign U.S. windstorm season, a recovery of investment returns, favorable foreign exchange rate movements and improved pricing conditions.

“A series of large losses that occurred in the first quarter of 2010 have worsened underwriting performance for both primary and reinsurance participants,” said Martyn Street, an associate director in Fitch’s insurance group, in a statement.

But although Fitch expects Lloyd’s earnings to decline in 2010, it said it believes the market will remain profitable.

Fitch added that the work of the Lloyd’s Performance Management Directorate, which reviews and controls the performance of syndicates at Lloyd’s, had resulted in reduced volatility in the market’s results.

Fitch also affirmed the A long-term issuer default rating of the Society of Lloyd’s, and the A+ insurer financial strength rating of Lloyd’s China.