According to Shelter and National Landlords Association an owner can sell their property but cannot evict the tenants if they still have time left on the tenancy contract unless the tenant has breached the contract, e.g. is in arrears with rent. The landlord can sell with the tenants in situ and the new owner takes over as landlord and then renegotiates the tenancy agreement when is is due for renewal. If you believe you have not breached your tenancy refuse to leave until the landlord has a court order telling you you have to move out. That will not be granted if you have not breached your tenancy agreement. You will have the right to remain there until your current tenancy contract expires. After that the landlord has the right to evict you by refusing to negotiate a new one.