There really isn't a traffic surveillance to be used on tablets in the UK, or better Europe. Save your money, features like GBT and WX via 1090 or UAT are US only. If you encounter GPS reception problems, you may get an external GPS, but in 95+% the built-in of the cellular iPad and iPhone will do the job just fine.
There are some experimental things going on and you may like to talk with the tinkerboys doing Stratux/Pilotaware/Flightbox, but do not expect much from it.