Well, if they are goods acquired abroad by purchase, they aren't a gift. So long as the material being exported isn't a weapons system, software, etc., I wouldn't think our customs service would care. It would be HM Customs you'd have to worry about, and I imagine they are not to be trifled with.
Also, there are excess baggage fees if you go over a certain weight. Add that to the fact that your (heavy) luggage will be tossed around the tarmac like so many holidaymakers samsonites and it sounds like a bad proposition.