sue the LL for what?NewShadow said:If he hasn't been paying council tax the council could chase you for the amount owing - if it's in your contract it's included you'd have to pay the council then sue the landlord via small claims.
If it is an HMO then statute law says the LL is liable for the whole council tax. Nothing can be disputed over that, its the law.
This is incorrect - in law there are two different tests to be applied - a property may be an HMO and require a licence under the Housing Act 2004 but not be an HMO for council tax liability purposes OR a property may be an HMO for council tax purposes but not be an HMO under the Housing Act 2004.
you then say "if its in your contract"... well then, the tenant has agreed with the LL in writing to pay £x as a "contribution" to the LL in respect of the LL's CT liability.
Failure to make such a payment is a contractual dispute been the LL as plaintiff and the tenant as defendant.
The judge will read the contract, decide how clear it is, decide how fair it is, and find in the case of plaintiff since it categorically says pay £x and I'll bet the wording is clear.