I've been to the Leicester show for most of years its been going and I can't remember them ever having a mandolin on display. Go by all means, but be prepared to be disappointed. The best place on earth for mandolins is the Acoustic Music Company in Brighton. They have a nice Nuggett in stock for a shade under £13,000 but I suspect that is possibly out of your price range. Luckily, they have many others at a lesser figure and Trevor's advice is always free.
Ray