I'd only be up/over there the odd time, for leisure these days. I did work in that London for a while during the recession, now that you mention it I should still have a UK Sim somewhere... but it's a bit of a faff if you're just going over the border for a few hours or whatever... we're all used to using our phones for everything these days... I guess, in the absence of some reciprocal EU style deal we'll just have to do without and download the relevant maps before we cross the line.