There is a list of Anglican Religious Orders and you’ll have scroll down to the bottom to find the ones in the UK (unless you fancy a few days in the Solomon Islands!). Most of these houses have guest accommodation.
A map of (Catholic) Benedictine houses in this country can be found here and a more useful list is here.
A more general list of Retreat Centres (which are mainly not part of a monastic foundation) can be found at the Retreat Association website.
I go to Burford Priory, but they are in the process of moving at the moment as you’ll see from the website! If you’re interested in what the old place looked like, a load of photos can be found in two of my Flickr sets: Buildings and Grounds.