PLEASE NOTE THIS IS NOT LEGAL ADVICE! You must seek legal advice on these issues.
Withholding service charges is a dangerous game leaving residents wide open to forfeiture. Most (if not all) leases have clauses in them saying if you do not pay service charges or money owed the freeholder can forfeit your property. It is a contract and if you break the terms then you lose your home.
The same should be the case for the NHG aspect of the contract, but the only place to enforce the freeholders obligations is the LVT Property Chamber which goes in favour of the freeholder in the majority of cases (see youtube clip at bottom).
All legal advisers will advise you to pay, but when doing so, write a letter explaining that you are paying under dispute.
There are other things you can do as well:
Stay in contact with Genesis Residents who are continuing to support many leaseholders with major problems with NHG. Our e mail is firstname.lastname@example.org
All of the residents in dispute need to make a face to face appointment at the surgery of their local MP. The more of residents that can attend as a group, the better. Their are currently 152 MPs on the All Party Parliamentary Group (APPG) for Leasehold Reform. If your MP is not on please ask them to join it. If they are on it already then the MP will want to hear your stories. Keep on making appointments. The more MP’s that hear the horror stories about NHG the better they can represent you especially if they sit on the APPG for leasehold reform. They can then do something about it if they know your situation.
Attend the Leasehold Roadshow at the Novotel in Hammersmith on the 4th September 2018 (this is next Tuesday). Its free and is a MUST for all leaseholders, shared ownership or not. It is popular so you need to book a space using this link. Take a copy of your ease and book a slot with one of the many leasehold specialists for their free advice. There are also around 6 talks on different aspects of leasehold.
Book using this link https://www.theleaseholdroadshow.co.uk/hammersmith/
Join the National Leasehold Campaign who are taking huge strides in the battle for Leasehold reform. Fill in all the surveys and sign all the petitions as these have been used by the law commission in the current recommendations for reform and this is still ongoing.
We do have a voice, use it! https://nationalleaseholdcampaign.org/
Download and read Louie Burns simple guide to leasehold. Louie is a legend and has been battling for the rights of leaseholders for over 10 years but things are moving in the right direction finally. His book is on Kindle only and all proceeds go to the Leasehold Knowledge Partnership who sit on the APPG for Leasehold reform.
It is also Louie Burns whose company put together the Roadshows to help leaseholders and all for free https://www.amazon.co.uk/leaseholders-simple-guide-leasehold-ebook/dp/B07DZPFKH6/ref=sr_1_2?ie=UTF8&qid=1533891246&sr=8-2&keywords=leaseholders+guide
Watch this 8 min clip on the outcome of a leaseholder who withheld payment and took his freeholder to tribunal.