Join Date: Nov 2013
Location: NYC / TYO / RSW Up in the Air avoiding the Snowflakes
Programs: UA GS 1.8MM, AA 2.1MM, EK, BA, SQ, CX, Marriott LT, Accor P
Posts: 8,058
We've done this a lot and it's quite straightforward - our process:
1. Freshen up in the arrival lounge
2. Take the Heathrow Express to Paddington, turn left and go up the escalators and grab a taxi to St. Pancras (Note that Paddington is under construction currently -- just follow the signs on the floor)
3. Check in -- you will do exit immigration for the UK and entry for France
4. Grab a coffee, glass of wine / champagne in the waiting area and wait for boarding
5. Enjoy the quick trip.
6. Walk of the train in Paris free and clear...
It may sound more complex than switching terminals at LHR -- but we find it more relaxing by far (but we've done it a lot so it's not stressful).