European judges have rewritten the rule book for insurance companies by banning risk assesment based on gender.

Setting insurance premiums on the basis of differences between men and women has been ruled to be discriminatory by the European Court of Justice. Insurers claim the judgment means female drivers under 26 in the UK could face a 25 per cent rise while men could see a fall of 10 per cent in their car insurance rates.

To date, discrimination in setting insurance rates has been explicitly permitted under EU equal treatment rules, "if sex is a determining risk factor... substantiated by relevant and accurate actuarial and statistical data".

The verdict - which applies from December 21 2012 - will force changes in the current standard practice across Europe of basing insurance rates on statistics about differing life expectancies or road accident records of the sexes.

The judges followed advice from the court's Advocate-General that "higher-ranking" equality provisions set out in the Charter of Fundamental Rights of the Lisbon Treaty must now apply.