Foe those interested, the list of permitted activity when on a short term business trip to the EU from January 1st. (For anything not on this list, you might need a work visa):
I should say that beyond what’s listed here what’s allowable and what isn’t varies by member-state.
One way to avoid all of this hassle is of course to have both a UK and an EU member-state passport.
(I do not, alas.)
(I do not, alas.)