does anyone know how service charge works in an la block?
Not hugely different to normal blocks for the 'normal' service charge for lifts etc. EXCEPT there is no 'sink fund' so if something needs doing i.e. new windows you get hit with a 'major works' notice. Do some reading about this as it can be an issue. Also see who is the freeholder/mgmt agent as they vary in quality.
You may struggle to get a mortgage on certain types of blocks. Typically OK under 4 floors high, can't be concrete construction and needs to be a certain % privately owned.
Also watch for blocks with communal heating because as a low-heating user (at work a lot, out a lot in evenings and weekends) I hated the idea that I would be subsidizing people sitting at home all day with the heating on.