This is a tricky question made more difficult by the fact that the answer keeps changing as the government introduce new rules or update and vary the old ones as to when a Section 21 notice purporting to trigger the termination of an assured shorthold tenancy is valid. The government is supposed to be abolishing these notices altogether but as at 29 September 2019 when this was written they had not done so.

The best way to answer this question is to visit the Nearly Legal Flowchart page where you can go through the steps set out to establish whether particular notice might be valid.

For more information on the related subject of tenancy deposits visit the Justice of Tenants site