If it's very worn so that the writing/legends are hard to read, and the main details are also showing wear then i think you'd be looking at about £2.00 max, maybe a tad more, but nothing over a fiver. If the writing legends are practically all gone then a £1.00 is about right. Now if you were to clean it you'd be lucky to get 50 pence. Thus definately don't clean it, and you might as well hold onto it, call it a good look charm or a conversational piece, or even a coin you keep for flipping. You never knew something almost 200 years old could be bought so cheap!