A section 21 notice might be invalid if there are mistakes in the form 6a or if the landlord hasn't satisfied their obligations at the start of the tenancy such as registering the deposit in a deposit protection scheme or giving tenants copies of the property's Energy Performance Certificate, gas safety certificate (if applicable) and the government's 'How to rent' guide.
Moreover, a section 21 notice can't be served if:
- it’s less than 4 months since the tenancy started, or the fixed term has not ended, unless there’s a clause in the contract which allows the landlord to do this
- the property is categorised as a house in multiple occupation (HMO) and does not have a HMO licence from the council
- the tenancy started after October 2015 and the landlord has not used form 6a or a letter with all the same information on it
- the council has served an improvement notice on the property in the last 6 months
- the council has served a notice in the last 6 months that says it will do emergency works on the property
- the landlord has not repaid any unlawful fees or deposits that they charged the tenant