Auto Insurance Claims: insurance time limit, unfair claims, written explanation

Question
how long does an insurance company have to investigate liability

Answer
The Unfair Claims Act in the various US states are similar and say the following: Every insurer shall complete investigation of a claim within 30 days after notification of claim, unless the investigation cannot reasonably be completed within the time. If the investigation cannot be completed within 30 days, and every 45 days thereafter, the insurer shall provide the claimant with a reasonable written explanation for the delay and state when a decision on the claim may be expected.

I am unsure what the law or regulation is in the UK.