The company also expects the performance of Confused.com, its UK price comparison site, to be weaker in the second half.
Admiral saw its turnover fall by 3% in the third quarter compared to the same time last year, the company said on Friday.
Admiral’s UK rivals include RSA, Direct Line and esure and other increasingly popular price-comparison websites.
Chief executive Henry Engelhardt said: “We anticipate that future earnings will be impacted by the decline in premiums experienced across the market in recent years, coupled with a return to higher claims inflation,”
Turnover at the group, which includes brands such as Elephant, fell to £513m while its UK car insurance turnover fell to £419m which was a 5% decrease. There was a 10% increase in group customers to 4.03 million compared with the third quarter of 2013, and also UK customers rose to 3.18 million which was a 5% increase.
The company also said that the performance of its UK comparison site, confused.com, is to be weaker in the second half of this year compared to the first.
Analyst at Shore Capital, Eamonn Flanagan, reiterated his “sell” recommendation on the stock, citing a “deteriorating” claims environment for the sector.
The Admiral results came a day after competitor Aviva announced that the number of traffic accidents staged by criminal gangs to generate money from whiplash compensation, is at an all-time high.
Fraud is already 21% higher so far this year when compared to the whole of 2013, the insurer mentioned, and greater than 50% of fraudulent motor injury claims it was detecting had been made by organised gangs.
The majority involve “crash for cash” incidents involving fraudsters who either deliberately crash two of their own vehicles together in a private place or brake sharply in front of an innocent driver’s car in order to force the driver to go into the back of them and crash.
Compare Car Insurance Providers and Save Up to £200