A comprehensive policy now costs 815 pounds on average, according to the latest index from price comparison site Confused.com in association with insurance broker Willis Towers Watson.

The index climbed 4% in the fourth quarter compared with a year earlier.

British motor insurers have been struggling with high costs, tougher environmental rules as well as a threat of tariffs on car imports and exports, if a post-Brexit trade deal is not negotiated with the European Union before 2021.

"Many of the challenges observed throughout 2019 will persist in 2020, as cost pressures remain from expensive vehicle repairs, theft claims, last summer's discount rate change, Brexit-related uncertainty and IPT increases," Graham Wright, UK lead of P&C Personal Lines Pricing at Willis Towers Watson, said.

Insurance premiums have remained volatile for a fifth straight quarter, Wright added

The index, based on price data submitted by customers to insurer Admiral Group's Confused.com, showed the annual cost of comprehensive car insurance increased across the UK, with motorists in Inner London hit by the sharpest annual rise at 8%.

Based on demography, premiums for female drivers aged between 26 and 30 rose the most at 9%. Male drivers aged between 17 and 20, whose premiums rose 6%, continue to pay the highest premiums.

Key players in Britain's highly competitive insurance sector include Admiral, RSA Insurance Group Plc, Direct Line Insurance Group Plc, esure and Hastings Group Holdings Plc.

Hastings said on Friday it expected annual earnings to plunge 42%, as claim expenses rose in the fourth quarter.

(Reporting by Samantha Machado in Bengaluru; Editing by Vinay Dwivedi)