And of course what your nationality is.
Maybe you have a fiche S.
In the ‘treat others as you would wish to be treated’ vein, the UK may be setting the bar
I expect that world unfolding events will in the near future render the concept of freeflow borders a bit of a pipe dream.
Best to travel with all the relevant documents, and those up to date.
But that has always been the sensible thing to do, so no change there then. 
True. Best to expect increased controls and not to be feisty regarding passport stamps or random questioning 