HowlingGale
Head Pro
They can but its illegal, and it isn't what everyone else does. A decent company will have a procedure for setting up home working which includes a lot of input from the Health and Safety team. "What is the right desk/chair combination for sitting there for 8 hours?" If a company doesn't include H&S, any issues raised by a staff member, e.g. bad back... I'm sure you get the drift.
Didn't realise it was illegal but in fairness I don't think they had time to consider legalities.
My back is aching at the moment. FWIW I've got an orthopaedic chair at work and that was about £500.