Flying to London next week. Have used Ray's Limo service several times in the past and were pleased. No answer to his web site 10 days ago, and two emails this week, so giving up on that.

Now looking at Just Airports, but they say I have to put in a zone for where we are going in London. How do I find that out?
We are staying at the Hyatt Churchill near Marble Arch.

Those who have used JA, do they wait a few minutes while you take cash out of the ATM?

I am not an expert on this but I believe Marble Arch is in zone 1. thereyet

Here is a link.
http://en.wikipedia.org/wiki/London_Underground
thereyet

I think it is the postcode that they need. Or part of it. in the case of the Churchill it would be W1

Vervid is correct. The whole post code is W1H 7BQ