If it is a lease / rental, make sure you’re careful not to leave anything around during ‘inspections’ ( the landlord has to inform you when they are happening, well in advance) and stash the bike(s) in the bike shed / outside, when the inspections happen.Good morning,
As it is a flat I would assume it is leasehold and some may say that I am being paranoid. :-)
Check the lease vary carefully for terms that prohibit the storage of bicycles within the flat, if they exist and you ignore them they can be grounds for lease termination.
It is true that it is incredibly rare for domestic leases to be forfeit for violations but it is legally possible and if the freehold owner does invoke such a clause legal bills would get terribly expensive very quickly.
If the the flat is in a block where the lease holders also own part of the freehold then such issues may be less likely, if the flats are run by a management company then enforcing the lease terms may just be policy.
If nobody complains then all will be fine, but one tenant with an anti-bike stance may make it an issue and the management committee/company would be obligated to act.
You say that that the new build will have a cycle store, this makes a clause such as "Bicycles must be stored in the cycle store" quite likely, rather than or in addition to a clause that says "Bicycles, motorcycles and similar may not be stored within the property"