Rory, what do you know about your clients? Many well-heeled Chinese enjoy golf, so perhaps a Pringle golf sweater, or cufflinks from Aspreys? Do they like horseracing? Then possibly a small antique print of one of the Classics winners? You could do worse than to ring up Harrods Gift Service and ask them to prepare a hamper (or hampers) containing typically British items, such as Gentleman's Relish, Scottish shortbread, Carr's water biscuits, hot English mustard, Piccalilli, smoked salmon, Lea & Perrins sauce, Bombay Sapphire gin, and anything else they can think up within whatever price range you have in mind.
Of course, if you're on a tight budget, then I suggest a different insight into the British culture you'll be representing:
Tins of mushy peas and baked beans
Jars of pickled eggs , Marmite, Bovril
A 6-pack of Irn Bru
Bottles of Ribena
A few flags of St George and some En-ger-land sponge hands to wave.