As Carolyn has found out, service charges seem to be the new PPI - a scandal which may well go on for maybe, 10 or 15 years.
They must provide accounts - invoices etc for the work booked to service charges. See Section 22 of the Landlord & Tenant Act 1985:
Main front page for the Act:
i.e. they can't simply pump up the costs and demand payment.
We should be demanding the paperwork and for back payment for serice charges if they cannot provide it. N.B. There appears to be a 6 months cut off period, a problem which we will need to ask the Government to deal with.