If you wish to divide your property you must create brand new leases for each flat, with Land Registry compliant drawings in place
Regarding leases, Landlord and Tenant common law stipulates that the landlord and Lessee must be separate entities. This is often seen when, for example, the owner of property may want to retain his freehold and leasehold titles in his same name, but this will not be possible and seen as void by the land registry. A solution is often to keep the freehold title in his personal name and grant a lease into the name of a limited company (wholly owned by the freeholder to retain control) or vice versa.