Earliest a Section 21 Notice can be given

Possession - Section 8 and Section 21

Hello Everyone,

Would welcome and appreciate any feedback to the below.  Thank you. 

The initial lease was done 22nd September, 2020 (the rent having remained the same throughout)

However, with the increase in prices, mortgages etc., we had to increase the rent last year for the first time.  A figure was mutually agreed by both of us (still below what it could have been however, accepted by tenant so we proceeded accordingly)

We took this opportunity to update all our paperwork and use the current NRLA lease being that the old NRLA lease was 3 years old and would have had updates since to it.

Everything is on the same basis, nothing has changed, other than the new rent.

The tenant has contacted us last week and told us she wants to apply for a council house  as the rent is too much and wanted a letter from the landlord. We assume she wants a Section 21 Notice to be given.

My question is even though the tenant has been there for over 3 years, as the new lease only came into effect on  29 September 2023, when is the earliest we can issue a Section 21 Notice.

Thank you.