score:7
That's a safety margin of 40 minutes, which, given London's usual traffic chaos issues, I would personally consider too slim
(I'm very cautious about missing flights).
I would either:
Again, this is personal caution. You'll probably have no problem.
Also, have you looked at advance train tickets? They might be a lot cheaper.
Upvote:3
An update for the beginning of 2020. The National Express's website says:
For airport journeys we recommend allowing at least 3 hours (180 minutes) between your coach arrival time and scheduled flight.
So 40 minutes margin is certainly too small as per website operators.