Kim has been to a number of retreats now - all slightly different. Here are her recommendations based on her own experience. They are all reasonably priced.
Other UK Based Retreats
Zenways do a 3 Day Breakthrough to Zen retreat. 3 days of working very rigorously with the question 'Who Am I'. It's not run like a full on Buddhist retreat but it IS full on. We put all our beliefs and notions about who we are under the microscope. As a part of the process we have the opportunity to shed a lot of unhelpful thought tendencies and the possibility completely exists for us to come up with an answer to the question that not only satisfies us but is beyond anything you could ever imagine or think ;)
www.westernchanfellowship.org Mostly Peak District
They do all sorts of different retreats so do have a look and see if there's something that grabs your attention (and do it!). Run along stricter Buddhist guidelines so expect early starts, chanting and lots of meditation. They do a version of Zen Retreat above although they call it the Western Zen Retreat. It's similar but a bit less intense and run over 5 days. They do other retreats too. Kim's done the Silent Illumination and Shattering the Great Doubt retreats and would recommend anything they do.
Kim did her very first retreat here. They have all sorts of teachers from all sorts of backgrounds so timetables etc are all slightly different. There is an emphasis on silence, though, and it's generally run along Buddhist guidelines.