Sorry, but you will need to spend some money to fight on Leighton Grove. Find out which properties were covered by the archetype survey, and which are in the contract with you. Then set up a Recognised Tenants Association (RTA) of leaseholders (see https://www.camden.gov.uk/ccm/content/housing/council-tenants-and-leaseholders/homeownership/getting-involved/) with whom you can make common cause. (Try and keep the tenants on board too throughout as it will make life easier). Hire a surveyor to comment on what Camden proposes using RTA powers; you can access one through the Leasehold Advisory Service site (lease-advice.org) and you could try advice from Tower Blocks UK, as they deal with fire issues and may be able to suggest one interested in that area.
Millman Street is, as far as I know, a heating system and so whilst an RTA is likely to be helpful, will need different advice.