If you have bought a flat, you have bought a leasehold interest. This means you have the right to live in your home for a certain period without having to pay rent, except for a small ground rent. The period is 130 years from 1 January 1981 and is set out in your lease. As a leaseholder you only buy the right to live in your own flat and so you also have to pay a share of the costs to upkeep and repair the building and the estate where your flat is situated. Tenants also pay their share of these costs through their rent to the council.
For an independent guide to your rights and responsibilities as a leaseholder, read Living in Leasehold Flats (pdf) produced by The Leasehold Advisory Service (LEASE).