Rubbish... lots of items could be swapped.. there is no unique solution.

Not rubbish- I agree it's not unique- it is really best if there is only one way a grid could go- having one big theme is such a great idea but it makes it really hard as a setter to separate the groups and make sure they can only swap as red herrings rather than a full replace/ exchange. But hat's off for trying it- it's not easy- is this a first attempt? I don't remember the name. I still enjoyed trying to untangle them. Good luck on your future grids :)