I recently flew LHR-JFK on a D fare and had the following experience:

Diamond Line couldn't book it, nor were they all that familiar with it. They ended up finding the same link I found here on FT and gave me a phone number for Tri-Star Worldwide.

The US based Tri-Star agent wasn't that familiar with the Delta part of things, but gladly took my reservation, taking a credit card "only to hold the reservation". The next day I received a call from Tri-Star wanting my ticket # and class of service. Apparently the first agent didn't set-up my trip as a Delta ride.

Day of service was great. The driver was early and called my mobile # back in the US to tell me he was waiting. Brand new MB E Class Car. Trip from central London to LHR T4 took less than a half hour.

A week later, my AMEX has been charged for the service. I now need to call DL and Tri-Star to sort this out.

How can Delta expect to attract more HVC pax LHR-JFK-LHR if it can't get it's car service right? Perhaps Virgin, who is more known for this perk will take things over from Delta in terms of managing the car service program? It isn't like Delta promotes it either.