Not too sure there are many unis that do purly electronics. Most do electrical and electronic. Tbh though with enngineering any uni ranked in the top 20 even 30 are good enough, but the best probably:
UCL, Cambridge, Southampton, Edinburgh, Imerial. But then again, i would consider surrey, manchester, bath, loughborugh, strathclyde, newcastle to be up there aswell, so it just depends really. Most are good.