I work from home and occasionally it would be useful to have someone take care of my DC (2yo and 3yo) for a day or two when I have a lot on or big deadlines. It's the sort of thing I wouldn't know I need much in advance.
I've used Sitters.co.uk a few times for evenings and once for a full day when I didn't know what else to do, but it didn't seem like a great solution for the full day. I'm in SE London - are there any agencies around or something like that?