Terms of a lease

[fitz]

I have recently become the freeholder of a small block of flats. The terms of the leases include a clause which states in respect each lessee,

“Not to assign underlet or part with the possession of any part or parts of the demised premises and not to underlet the whole of the demised premises”

The previous freeholder did not enforce this clause and over a period of years some of the flat owners have rented out their properties
Has a precedent been established which will prevent me as freeholder from now enforcing this term of the lease. And if I am entitled to enforce it what would be the necessary procedure to do so.

[someone]

This is a legal question, not a tax question.

Absolute bans on subletting are rare in leases but can be enforced. Most have a 'not unreasonably withheld' landlords consent needed.

A majority of leaseholders could get the lease condition amended but not an individual.

The leaseholders could also try collective enfranchisement.

Is letting causing a problem - airbnb perhaps? A clause about 'residence for the use of a single family' also rules out commercial airbnb (as opposed to a single let once per year while the family are away on their holiday)

I am neither an accountant nor a lawyer!