http://www.reactionengines.co.uk/
Reaction Engines Ltd has been at the forefront of the development of technologies for reusable spaceplanes for over twenty years. REL is both expert and experienced in space transportation generally, and in the engines for reusable space launchers specifically. In particular, REL is a world authority on heat exchanger technology for the engines of advanced reusable space launchers.
By applying a combination of established physical principles and innovative engineering design, we intend to develop a range of products that will enable the commercial exploitation of space.
REL is based at the Culham Science Centre in Oxfordshire in the UK.
http://en.wikipedia.org/wiki/Skylon_(spacecraft)