I am a leaseholder and this kind of thing is a complete racket. If you get enough leaseholders on board then it’s possible to invoke the leaseholders’ right to manage but it’s an admin hassle to set it up. If there’s a residents association that is usually the best forum to start these things - if there isn’t then setting one up may help, but it is time consuming, you need volunteers who can devote some time (and ideally some expertise in administration, basic accounting etc) and inevitably there are costs (low to actually set up a residents association, but potentially high if you need to instruct lawyers, which becomes more likely if the landlord starts not playing ball with the association).
It’s worth looking at the leasehold advisory service to get a view of how things are supposed to work, but as stated before, the terms of your specific lease will give the exact situation.
Ultimately at my place the leaseholders acquired the freehold (becoming our own landlords) and so were able to dig down into the service charges, ultimately saving ourselves a packet by changing management company (we thought it was too complex to self-manage the property so decided to continue with having a managing agent). All kinds of under-the counter stuff was going on, for example the old management company was receiving a 20% kickback on the building insurance premium from their preferred insurance broker, which of course was paid for by us leaseholders through service charges.
As an individual leaseholder your ability to challenge anything to do with service charges is fairly limited, you have a better chance through something like a residents association, where all leaseholders are represented by a single body. Residents associations have their own problems and often get bogged down in petty shit, but it’s worth thinking about if your service charges are escalating as much as you’ve described - unlikely to get any better if the leaseholders don’t take any action.
