So Warwick Castle is usually mega-pricey. But I have found this Carol Service that is only £5 per adult (£1 per child) which all goes to Chariddee. I don't expect that it includes a proper look around the castle as the pictures seem to show everyone outdoors but it is such a spectacular castle even from the outside and I just thought I would share.
Nothing like a rousing carol service to get in the Christmas spirit 
www.carolsatwarwickcastle.co.uk/bookings.htm