http://www.direct.gov.uk/en/HomeAndCommunity/Privaterenting/Problemsanddisputes/DG_189241
"Ending a tenancy early
If you are seeking possession because your tenant has not paid the rent or has broken one of the other terms of the tenancy agreement, different rules apply, depending on which type of tenancy your tenant has. For example, if the tenancy is an assured tenancy, you will need to use one of the reasons or 'grounds' for possession in the Housing Act 1988.
If you use one of the grounds from the Housing Act 1988, either two or four weeks' notice may be required. Some grounds are mandatory – this means the court has no choice but to make a possession order if it is satisfied that the ground exists.
Examples of mandatory grounds include:
- more than eight weeks' rent arrears (unpaid rent)
- repossession by mortgage lender (eg the property you own and rent out is being repossessed)
Other grounds are 'discretionary' – this means the court will look at the reasons and decide if a possession order is fair.
Examples of discretionary grounds include if the tenant:
- often pays rent late or does not pay rent
- breaks the terms of the tenancy agreement
- is a nuisance to neighbours
- uses the property for illegal purposes (for example, dealing drugs)
If the tenancy is regulated, possession can only be sought using one of the grounds in the Rent Act 1977.
Break clauses
If there is a break clause in the tenancy agreement, you can then give notice (usually two months) at any point, which ends the tenancy early.
However, a landlord does not have a guaranteed right to possession during the first six months of the tenancy."
So basically, they probably haven't got a leg to stand on and are threatening you with an illegal eviction.
What type of tenancy do you have? How long have you lived there? Have you ever had any problems before?