Why does it matter if you're only meeting one W/G?
External Link/Members Only, currently I don't do out-calls.
But If I did, I would meet the W/G out-side first to make sure its who I booked.
So if there an issue, with B&S or, I'm not happy. I could just walk away with out her knowing my room number.
IMO, in calls are much better/cheaper (less risk). Most of the Hotel in Heathrow are only a short walk, bus or taxi ride away.
Lots of options are around, IMO.
I find if I walk in the area, is very easy to call plan B/C/D etc.