Please help to find more leaseholders, especially ones who are non-resident:
1) Visit https://nethouseprices.com/house-prices/portpool%20lane,%20london and https://eservices.landregistry.gov.uk/eservices/FindAProperty/view/QuickEnquiryInit.do and enter the postcode for your block. Postcodes include EC1N followed by 7UB, 7UR, 7SN, 7TY, 7UD, 7SP, 7UE, 7UH, 7UL, 7UN, 7UQ, 7SD, 7SR, 7UP
2) For the first link above, these are addresses of flats sold since 2009 and therefore a leaseholder now owns it. For the second link above, where it says "Tenure: Leasehold Price Paid/Value Stated Data: Yes" after doing a search it means a leaseholder owns the property.
3) Meet the residents of the flat and ask that the leaseholder contacts the group.

Free Leaseholder Advice (Book a free 15 minute call to have your questions answered and read general help)
www.lease-advice.org

Marlborough Knightsbridge Management Limited v Thierry Gilles Fivaz (Landlord cannot force tenant to change a door as part of improvement works)
https://www.judiciary.uk/wp-content/uploads/2022/07/Marlborough-v-Fivaz-judgment.pdf

Waaler V London Borough of Hounslow (Comparable case where the leaseholder won)
https://decisions.lease-advice.org//app/uploads/decisions/act85/12001-13000/12581.pdf

Florrie's Law (£15k cap on some types of major works by councils)
https://www.lease-advice.org/article/mandatory-capping-of-major-works-service-charges-for-leaseholders-of-social-landlords-in-england-florries-law/

First Tier Tribunal (Property Chamber) Application Forms
https://www.gov.uk/government/collections/residential-property-first-tier-tribunal-forms

Camden Leaseholders' Forum (Discussions by leaseholders from across the borough)
https://www.leaseholdersforum.org.uk