You can patent a design concept (provided it is truly original) . Look at the Patents Office website for details, and what similar concepts have aleady been pattented. It's not expensive to do it yourself, but beware, once your patent is published you need to maintain it with annual payments to prevent anyone else from seeing on the Patents Office website and copying it once your patent lapses.
I did it with a design, but as soon as I found Virgin Cola and other large companiew weren't interested I gave up my idea. Then a cheap copy of my idea was rushed out for the Christmas gift market - there was nothing I could do. Probably lost me the oportunity to make a few quid.
WARNING: Avoid some of those "invention" marketting companies that rip yopu off to give the sort of advice you could find out yourself from a good trawl of the internet.