The newish Camden Council Service Charge Guide (pages 17 and 35) might be of use. Also the Leaseholders’ Forum have created two guides which explain about heating upgrades and the gas system that Camden Council uses:
Personally, I’m in in favour of individual systems and have not yet heard of any estates that love their communal systems…
p.s. I believe, if you really want, you can contact the Leaseholder Services team to visit their offices and see the actual invoices. Whether this makes them good value, is an entirely different matter!
Best regards and good luck!
Leaseholders’ Forum member