[Lee]

I have the same set, bought from Argos so branded differently. If you put the chocks in place upside down, they appear to work, but collapse once any sort of pressure is applied, however if used correctly, they're fine. On first use it's difficult to work out which is the correct way.

 

[Lee]

One side is flat, with a little raise bump either side, the other side is slightly curved. When you open the chocks, a metal flap pops down and sits just past the raised bumps. The pressure of the wheel then locks everything in place, however it doesn't work if they're the wrong way round. I've made a crude drawing to illustrate what I mean.

 

[Lee]

If used correctly they won't Dave. It depends how he used them.