Sorry this was directed at Danny Boy. Don't know what happened to the quote...
Not really. It's all a bit Alice in Wonderland to me. A coin, legal tender, which you would be crazy to spend at face value, but also be crazy not to accept if offered at face value for a good or service. Let's all work that one out. Regardless of the value question though I don't think you can disoblige a legal tender coin, otherwise what would be the point? I know only 20 pence of coppers, a fiver's worth -I think- of change are tender and more than that can be refused but for all practical purposes we'd all accept more if need be. Unless of course you were being vindictive and paying your council tax bill in pennies at the town hall, they'd probably refuse... but I have been sorely tempted to try it anyway, just to wind them up.
You certainly wouldn't disoblige a debt being paid in Gold and Silver Brits at face value if you had a clue and any sense, which sadly most people don't. Our collective memory of gold and silver as money, paid in full, is long gone.
There does seem to be a principle of law at stake with the issue though. Not that i'm a lawyer but I'm pretty convinced that someone with a lot of money and time on their hands could take HMRC to court on this. And win. Of course everyone would boo and say you were the bad guy denying HMRC of much needed tax money but that's another argument entirely!