We have just had a lovely time at a wonderful resource near Elstree, an adventure playground specifically for children with disabilities (lots of both inside and outside activities including a lovely, new playground, and all sorts of indoor equipment). It helped that it is a beautiful day! But if anyone is anywhere nearby I would strongly recommend it!
(no, I have nothing to do with the playground or the charity that runs it, I was just highly impressed and we had a great time!). They are trying to get regular Sunday as well as Saturday sessions off the ground and they do need support. It costs £5 an hour and I can't remember when I last spent a more worthwhile tenner!