While on my hols near Wells in Norfolk I spotted a cheap knife with a crooked blade in a hardware store (Walsingham's), priced at £1.89. It was "Blackspur" brand and had a serrated blade. I think it was meant for cutting melons into balls or similar.
Anyway, I bought one, and after 10 minutes at a bench grinder to get rid of the serrations and some stoning with a round stone I have a passable crooked knife. I've used it on a spoon and it works well, the only thing I need to do to it now is extend the handle nearer the blade, or maybe just make a new handle.