https://england.shelter.org.uk/housing_advice/repairs/repairs_and_inspections_access_to_your_rented_home
You need to allow your landlord access to your home to:
carry out essential repairs to the property
do an annual gas safety check
inspect your home for any repairs that need to be done
You don’t have to let your landlord in for any other type of inspection unless your tenancy agreement says you have to
Access for improvements
You don’t have to let your landlord into your home if they want to do improvements that don’t count as essential repairs.
Improvements could include:
fitting a new kitchen or bathroom
building an extension
redecorating or fitting new carpets
If you don’t want your landlord to do the work while you’re living there, you could ask them to wait until you’ve moved out
If you’re happy for your landlord to do the improvements but the work will cause you inconvenience, you could negotiate with the landlord:
agree in writing that the work will only take place at certain times
ask the landlord to provide alternative accommodation
ask for reduction in rent or other financial compensation
surrender of the tenancy with full refund of any Deposit