Thank you THEAMBLER, I really enjoyed your Thingy.
Apart from not getting B or G, I got J wrong too and just had it as TWENTY (although I know T isn't an unknown number! Nice devious clue.
I must also admit that when I first looked at it, I decided there and then I'd never be able to do it but it kept nagging at me until I had a go and got C.
Again, many thanks.