Hi Clem,
Lots of different things can cause a fire, old wiring is often a cause,especially when mice or rats have chewed through a cable then built a nest,also sadly a lot of stoves are left unattended with the grill or chip pan left on, also fires left unattended with clothing or inflammable material nearby, very sad thing to happen to anyone.
We had a call a couple of years ago to a council house,the mother had gone for a bath leaving her little girl downstairs
(wintertime) little girl thought her teddy was getting cold so she set a newspaper alight on the settee, luckily nobody was hurt, as we had just installed mains operated smoke alarms, Ray