These are charged to leaseholders every six months. There are full details of the process and documents involved in the Westminster Housing Lessee Handbook. At current costs, estimate about £2,500 per year for a two bedroom maisonette.
There is a scheme for Key Lessees: these are leaseholders prepared to spend time looking through all the detail of costs that go into the overall Service Charges and checking that they match the sub-headings on the final bill. If you are interested, contact (020) 7245 2106.