Leasehold Flat

My son wants to extend the lease on a first floor flat, will the owner of the ground floor flat have to do the same?

Gillian - I assume you mean extend the term and if so whether one or both do is a matter for them and the landlord to agree upon. 
In my experience it's invariably a good idea for all to do it at the same time both re cost, efficiency etc but one is not dependent on the other and you can have two different terms, one for each flat.

Thank you that was very helpful.