I was lucky.......Or I think I was :-\
I found an old terrex spade at the back of a second hand shop for £25. So I bought it.
I've tried it out on my allotment and it 'sort of' works. After looking at lots of pictures on the internet, I wonder if the torsion spring has been 'put on wrong'
It does seem to quite loosely fit in place rather than fit snuggly and seem different from any photos I've seen.
.........I do wonder if someone in their attempt to get it working properly has bent the spring arms to a new shape. ::)
I'll show you mine, if can suggest how to fix it!.
Or am I worrying over nothing and they are just weak pathetic springs?