Collective enfranchisement is the right for leaseholders of a building, or part of a building, to join together and buy the freehold of that building from their freeholder (landlord).
https://www.lease-advice.org/fact-sheet/collective-enfranchisement-buying-freehold-building/
https://www.respectmortgages.co.uk/what-you-should-know-before-you-buy-a-leasehold-home/