Shares in car insurance giant Admiral slid almost five per cent this morning after analysts delivered a gloomy verdict on the Cardiff-based firm.
Trading at 1,836p each, Admiral shares were the biggest loser on the FTSE 100.
JP Morgan analysts cut Admiral's target price from 1,980p to 1,900p and lowered its rating from "neutral" to "underweight".
In a note on the broader non-life sector, analysts warned of a "different pricing backdrop from the experience of the last few years, both in motor and commercial/speciality lines".
Motor insurers are keen for the government to follow-through on promises to clamp down on bogus whiplash claims and reverse a decision by the justice secretary at the start of last year to slash the insurance discount rate. Both of the issues have been blamed for putting hundreds of pounds on annual motor premiums and hitting younger drivers in particular.
But with many ministers focused on Brexit-related matters, insurers fear promised changes may be a long time coming.
Today, JP Morgan analysts said the wait for enacting the changes is likely to weigh on the stock market valuations of those insurance firms that are particularly exposed to motor claims.
Admiral rival Hastings was also downgraded by JP Morgan from "overweight" to "neutral".
Meanwhile, catastrophe insurer Lancashire was given an upgrade to "neutral" and JP Morgan picked RSA, Beazley and Hiscox as its preferred stocks in the UK non-life sector.