Most leases include service charges for either one-off repairs or a regular annual charge for maintenance. there are regulations about how a freeholder or managing agent can set charges and the best way to challenge them is by getting together with neighbours who have received the same charge.
Warner flats are unusual in this respect because usually there are no service charges apart from insurance. Warner leases usually say the responsibility for maintenance is divided 50/50 between the ground and first floor leaseholders. So if you receive a service charge, check your lease first. (You can a free legal advice on what your lease says from LAS.)