[efaref]

The legal limit for the security deposit is five weeks (or six weeks when the annual rent exceeds £50k).

source: https://www.gov.uk/government/news/security-deposit-cap-redu...

[gpderetta]

The deposit is max 5 week, but the tenant is still liable for any damage beyond the deposit. Of course the landlord need to take the tenant to court and there is no guarantee they'll ever be able to recover the money.