Definitely wasn't heavy handed with the leveling kit, in fact, it was only a gentle pull and the handle just snapped. The first few tiles went on well and didn't need much leveling anyway, I just put the clips in in case they did, literaly just nipped them gently so they were firm, on the 6th one, it the handles gave way. They are just lightweight plastic. I'm a computer engineer by trade, so I'm used to handling pliers of all sizes and types and not being heavy handed with them, these were just rubbish!
The replacement wheels arrived and I have fitted one and it all works again. I've looked at the old one but it looks identical to the new one, but the new one cuts nicely and the old one doesn't! I'm being very gentle with this one 🙂
Also found that some of the tiles are very convex and it is these that won't break. Wickes say they'll replace the lot or some or whatever we decide.