Morning RoyM
I use a trenching tool, I think its the 'German' model with a wooden handle, can be used with blade straight out, or at 90 degrees. They are about a fiver at surplus stores.
The 'American' all steel model is junk, it rusts away in no time, the locking threads go, they are scrap when new.
I have never seen the exact model illustrated, but it looks good. Google returned 2 hits, they seem to be made in Canada, but I doubt a UK stockist. You could always mail order from Canada or US, you should find a stockist on the Internet.
My avatar is a poor likeness.