Serving an eviction notice is the first step to take to repossess the property. Tenancy agreements normally have a start date and an end date. This is known as a fixed-term tenancy. Once the end date has passed, the fixed term has 'expired'. Once the AST fixed-term has expired an eviction notice gives you an automatic right of possession without having to show any reasons for wanting the property back.
A Section 21 notice is suitable if you just want the property back but are not looking to take action for rent arrears or money to repair any damage to the property. To use a section 21 notice the deposit must be protected in a government deposit scheme (if you took a deposit), you must serve the notice as landlord on the tenant (eg by first class post) and you must give the appropriate amount of notice (at least two months). For further information on deposit schemes read Deposit protection schemes.
You cannot serve a section 21 notice to have an expiry date that is the same as the end date of the fixed-term tenancy. For example if the fixed-term tenancy ends on 4 July, the expiry date on the Section 21 notice cannot also be the 4 July.
You can only serve the eviction notice once four months have elapsed, using a Section 21 notice.
Please note that in England there is a temporary ban on housing repossessions until 31 May 2021 except in extreme circumstances such as anti-social behaviour and extreme rent arrears of at least six months.