Most leases include service charges. This can be a regular annual charge for maintenance, and can include a contribution to a reserve fund for one-off costs. Leaseholders can also be billed for major works but these have to comply with Section 20 regulations.
Warner flats, of which there are 3-4,000 in Waltham Forest, are unusual in this respect because in most cases there are no service charges apart from insurance. Warner leases usually assign responsibility for maintenance to the leaseholders, divided 50/50 between the ground and first floor flats. So if you receive a service charge, check your lease first. (You can get free legal advice on what your lease says from the Leasehold Advisory Service (LAS).)
LAS also provides good fact sheets on service charges and how to challenge them.