I looked at Land Registry burdens so I think monthly running costs are much higher. One fourteenth of concierge salary, pension contribution, housing and maintenance cost, I estimate as 5k per year and one fourteenth of services cost, sewerage etc, approx 2k per year, index linked, then share of one off communal area maintenance costs, roads, trees etc.
Also restrictions on pet numbers and type of pet. Possibly Air-bnb style letting banned, no letting off parts like annex.
House insurance has to be proven annually and full reinstatement or site clearance, not cheap, probably 5 to 8k per year, e.g through Hiscox.