Thanks all for an interesting discussion on this one. I think my initial problem was possibly caused by lack of traction generally (it was frozen hail and had been compacted) and possibly because I was being a bit half-hearted about it (I was trying to get out of the way of a bus, but he looked as though he was going to have to change his mind anyway ...... he did, fortunately). It's quite a hill (not sure of gradient, as there are no signs, but my guess would be about 1 in 6)
My comment about proudly saying I have four wheel drive wasn't smugness or over-confidence about the situation as the roads weren't that bad generally (it was all very localised). I just didn't know how that elderly person who was probably going to tackle it in the wrong gear would fare. Once the sun had come round about an hour later, everything thawed and the roads round Dad's had dried out again by 3. They had the same there for three mornings running but 12 miles away we had nothing at all.
I expect you read about the awful coach crash in Cornwall on black ice on the 22nd December. There were isolated crashes all over the place as to be honest, we just don't expect the temperatures to fall that far (and although I didn't look at the forecast that morning, unless you get a very specific localised forecast, both the local and national weather forecasts just plonk a weather/temperature symbol on the map and it is most definitely not "one size fits all" down here). Doesn't excuse irresponsible driving in cold weather, but then again, driving at any speed even if it's 5mph, if you hit a patch of ice you're going to lose control of your vehicle even if only for a moment.
We don't really get a lot of slippy stuff where I live as we are too close to the sea, and when it does freeze, it's frozen rain which usually melts again if it rains again. In February when we did have a little snow a neighbour tried putting salt and some coarse beach sand on his drive but it had washed away by morning and he still couldn't get out without the loan of a bit of carpet (which he's still got

).
I always reverse into our drive (also sloping - need to do a survey on who's got a sloping drive

) but that's because if I went in forwards and reversed out all I would be able to see would be sky until I felt the impact of an oncoming vehicle

My Dad, whose drive is the same gradient as ours but longer, always reverses out - as BDC said, reverse gear usually gets you everywhere!!
Anyway, back to the "does 4WD work in reverse", it obviously does in the correct circumstances, so thank you, one and all.
I've had a pair of grip strips in the car for quite some time (pre-Bongo, and now in the Bongo) primarily to get me out of muddy gateways (again, usually avoiding buses) but have never, ever used them. I suppose they may have their uses on ice/snow but then again, the bottom surface would have nothing to grip on to.