Not a Giant Box 1/2/3 or anything from the Trek empire. Certainly has a Britishness about it such as Saracen or Falcon group. Saracen seems a possibility as they have made full aluminium URT designs. Nice component list if original so I'm interested to see what this turns out to be.
Its a DDG frame, and/or the same far east effort with what ever brand name you wanted to put on it, the trade were buying these at about £69.00 and selling them mail order for......whatever they could get. Normally £199 there or there abouts,