A couple of summers ago we stayed in a hotel called Redworth Hall, in Newton Aycliffe, about half an hour from Durham.
We had a family room and managed to get a good deal (which come and go quite regularly, particularly if you don't want to stay a saturday night) - certainly cheaper than staying in a UK Centre Parc.
It had a fabulous pool/leisure centre, a small indoor soft play, tennis courts, crazy golf, outdoor soft play, frisbee golf and more plus the family room we had (an ordinary one rather than a more expensive one) had plenty of space, almost like 2 rooms knocked into one so big one for dh and I with a big double bed, dressing table, space for a table and couple of chairs in the windows as well as separate arm chairs, then through a big arch to the other half of the room with twp single beds - separate from each other rather than jammed up together and a good sized nice bathroom.
Pool was lovely, warm, not too busy and within the hotel complex rather than having to trek through a Parc (handy if the weather is bad or you want to look down to see how busy it is or you just don't want to walk a long way there). Pretty much everything was free - a couple of things wanted deposits left if you borrowed rackets or clubs/balls/frisbees etc but you got that back when you returned the items, which was fair enough.
It was beautiful and in a stunning area, there were lots of things to do locally, from a railway museum to visiting a great Roman dig in the middle of nowhere, Bishop Auckland was about 10 minutes away, Durham was half an hour away, you were on the edge of the North Pennines, you were about half an hour away from the coast at its closest or an hour away from Whitby or an hour and a half from Bamburgh if you go back northwards.
There were lots of things we would have done quite happily but we didn't have time, also we wanted to have a relaxing holiday so didn't push to do everything, so were happy to relax at the hotel in teh pool and playing crazy golf. We ate in the hotel a couple of nights, out other nights. Nice big hotel breakfasts!
When we booked i looked at the usual websites and their own. Their own has good discounts but we ended up going with one of the big sites (maybe hotels.com?) that you could put in your email address for 'secret prices' or some such phrase - i did (usually don't like handing email out willy nilly!) and there was a good reduction that basically reduced the rate we paid down so we got b&b for the standard rate advertised for just overnight no breakfast. We paid maybe £80-85 a night for a family room on a b&b basis, which we thought was really good value for what it was.
The other thing to consider is looking at Centre Parcs in Europe - I've been to them in Holland and it was cheaper for us to get to Holland by ferry, pay petrol for a much longer trip, and an overnight stop in both directions to break up the driving than it was to get one in the UK. We found the facilities were much better too - we went to Het Heijderbos which had a fantastic second dome with a giant adventure zone, a bit like being in the Jungle zone of the Crystal Maze! It had caves, running water, rope bridges, tropical birds, zip wires, climbing things, amazing plants and things, a giant climbing /adventuring area, suitable for adults and kids and even a cafe in it - so much fun. The dc would have spent hours in there every day if they could...