I can’t find anything about the maximum that the service charge can increase by
That's because there isn't a maximum. Legally, all your service charge needs to be is "reasonable" and apportioned "fairly". And this is what a Tribunal will look at if you ever ending up going that far.
I suggest familiarising yourself with the a good understanding of service charges so you can ask the right questions if/when you get offered a property:
www.lease-advice.org/advice-guide/service-charges-other-issues/
Service charges (and sinking fund) calculations can be quite a complex area when you start getting into 'mixed tenure' buildings. By 'mixed tenure' I mean a mixture of resident types such as leasehold/shared owners and renters (tenants) whether that be social or affordable rent or market rent.
It's important to bear in mind that the service charges for newer buildings tend to be higher. Although they should need fewer repairs than older buildings, this isn't necessarily the case if there's been shoddy work done by the developer or the developer has used cheaper materials etc. Unfortunately this is fairly common. Newer buildings also tend to have more shared facilities (such as lifts or electronic gates) and these all need maintaining/servicing so the service charge increases as a result. All those lovely shiny things that make your building so appealing? It's going to cost you. Make sure you understand how the service charge is apportioned (ie.split between homes) before you sign your lease. The market convention these days is by size i.e. square footage/metreage but it's also possible to do it just by the number of homes or even number of bedrooms. It's important that you understand what you're getting yourself in to. It's amazing how many people don't. I know of quite a lot of developments that apportion by number of homes so someone with a 1 bed flat living alone pays the same as someone with a 3 bed flat and 4 kids. Of course the 1 bed flat owner hates this and think it isn't fair. But if you do it by size of property, the 3 bed flat owner pays more than the 1 bed flat owner which the 3 bed flat owner hates. Both methods are considered fair legally but it's worth understanding what method is used when you buy somewhere so you can feel comfortable with your share of the split.
If you're intending to staircase (make sure you understand the extra costs involved in doing this as it can be expensive), and/or be there a long time, make sure you understand what the sinking fund covers and how it's calculated. Find out what the current sinking fund is and ensure this is on track. You don't want to move in and then find out the whole building needs a new roof in a year but the previous sinking fund contributions have been too low so you're going to be hit with a big bill. A sinking fund is basically a long term savings account for major works/repairs such a new roof, new doors & windows, new lift etc. Some buildings don't have a sinking fund (!) or have very small contributions. This makes them look very competitive when you're buying as the service charges are low. However, this isn't necessarily a good thing as it means you can be hit by huge bills when work is needed. So sometimes a high service charge is actually a good thing if it's covering a prudent sinking fund contribution as you're basically paying a little more now to avoid being hit by a big bill in the future. Are you starting to see what I mean when I say this is quite a complex area?
I'm not trying to put you off but it's shocking how many people sign up for things that they have no understanding of. And then they get hit by bills higher than they can pay. I know some who've even taken their housing association to a tribunal over service charge costs because they think they're paying too much. This normally ends badly for them as legally a service charge just needs to be 'reasonable' and 'fair'. Despite what people may think, housing associations aren't trying to make a profit out of service charges. These are not-for-profit organisations. Your service charge will include an admin fee for the housing association which covers their costs for staff, HR, IT, etc.
Hope this helps a little.