Thanks for the replies doods and gals, I'm still processing them but am tending towards a "dry" (ie non-oil filled) electric radiator at the moment because i can't see what advantages an oil-filled one would have.
And as i see it, an oil one would take longer to begin heating the room because it'd have to heat the oil first.
Luckily I live in a small 3rd-floor flat which heats up quickly, but I might get some expanded polystyrene ceiling tiles so heat doesn't escape through the ceiling.
In fact most homes ceilings are too high anyway which means we're wasting cash and energy heating the empty space 3 feet above our heads, so I might try to get some really thick tiles i(f they make them), to fill up most of that space..