The London market opened higher, but shares in insurance companies slid following a change to how personal injury claims are calculated.
The change, made by the Ministry of Justice, affects the rate at which compensation payments are calculated, which could increase payouts and knock insurance companies' profits.
Direct Line shares fell 5.4% while Admiral Group dropped 4%.
Despite the falls, the FTSE 100 index rose 27.74 points to 7,271.44.
Housebuilder Persimmon was one of the top risers on the index, up 1.6%, after reporting a 23% rise in annual profits and giving an upbeat description of recent trading.
Shares in the London Stock Exchange fell 3.2% after doubts were raised over the prospect of its planned tie-up with Deutsche Boerse.
The LSE said the deal was unlikely to be approved by the European Commission, after it disagreed with the Commission's order for it to sell its 60% stake in MTS, a fixed-income trading platform.
On the foreign exchanges, the pound was weaker against most other currencies, with analysts putting the fall down to speculation about another referendum on Scottish independence.
Sterling fell 0.5% against the US dollar to $1.2404 and dropped 0.7% against the euro to 1.1724 euros.