I always come back from the old country with new tools, if I was going back tomorrow I would bring back the 18v Dewalt finish nailer as it is not available here. If you go for cordless tools then you don't need to worry about the different voltage. Have a look to see what's NAINA that you fancy.
I always put the tools in my suitcase and carry the tool box or systainer if its Festool as carry on.
Enjoy London.