bath stains at checkout

Tenancy Deposits

Has anyone any experience of this situation please?  Independent checkout inventory shows photos of stains in the bath. Tenant says there were there when they moved in 2 years ago, but independent checkin inventory with photos do not show or mention any. I would like to claim fair compensation from the deposit as I feel I need to replace the bath as the stains are ugly and will deter future tenants, but I do not know how much I can claim. I know I cannot claim betterment as the bath is at least 8 years old. A new bath of same type would cost about £160 plus fitter at £300.   I also want to claim for cleaning of the property as no attempt was made to clean, they just removed most of their belongings (inventories show discepancies so I hope that will be ok even though tenant was invited to checkout it was during the day and they couldnt attend as were at work), they also broke lampshades and a kitchen fitting. Any idea what percentage of the cost of the bath refit I can claim please?