We travelled today up the M11 and stopped at Birchanger Green services having had the air con set at 18C.

We were stopped roughly 15 mins, returned to the car and my g/f noticed dripping underneath the engine bay. I didn't examine there and then as I suspected something to do with the air con. We're talking a drip around once per second or every two seconds - I think it was water but only at a distance.

The car got us home without incident and made a subsequent journey again without problem. I'll check fluids again tomorrow morning (I checked before our trip, no issues).

I was imagining maybe condensation from the cold generated? Don't know how the air con system actually works but is it to be expected? Funnily enough we checked when we got home - no dripping at all. Very weird.

Yep, the evaporator generates condensation, it drains out the bottom.