SUCCESS!
Had a go yesterday and here's what I did/discovered. First of all, I have to SAKs, and as it happens one is a Victorinox, and the other is an imitation with the other style of tin opener. The target was a tin on beans.
My first go was with the Victorinox. By hooking the hook under the lip of the tin, placing the point on the inside and levering up, the point went in, starting the cut. I was surprised at how easy this was.
The action is then to slide the knife forward allowing the tip to rise up on the uncut edge until the tin edge is almost at the tip of the blade part. Then rock the knife by lifting the handle until the next length is cut.
Continue around until the lid is completely separated.
Flushed with success I moved on to the other knife. Starting the cut is exactly the same as the previous one:
Use the same rocking action as before, but this time draw the knife back towards you.
I found the second method much quicker, but the edge was much more serrated (I don't think this was due to my technique), and the lid didn't want to separate from the tin as easily.
My reward for all this hard work was a nice bowl of steaming hot beans for lunch
Shown here is my latest spoon, which is a really good user.
Thanks to those that explained well enough for me to have a go, and hopefully this will have helped a few others too.
Cheers
G