Hi,
Electric heaters are 100% efficient, so each kw of heat costs aprox 12p (if your on a good tarrif)
Oil boilers should be at least 70-80% effieicent, 1 litre of oil costs aprox 60p, you get 10kw of heat from 1 litre of oil so 1 kw from oil costs 6p (add in the efficiency difference then its just under 7p per kw)
Again LPG boiler should be 70-80% efficient, 1 litre of lpg costs aprox 55p, you get 7kw of heat from each litre, so 1 kw from lpg costs 8.6p (again add in the effieciency and you get about 10p per kw)
Only if you have a really old boiler will electricity be cheaper, either that or you are not heating you home to the same level (only heating half your rooms etc...)
Oil is currently the chepest method of heating you home off grid, only a wood burner of a heat pump system would be cheaper