>>what will it make it very difficult to get from the plane in T3 to security at T5?<<

It isn't difficult getting from one terminal to the other - not at all. Doing it in <B>25 minutes</B> is the issue. The two terminals are very far apart so the bus ride alone takes about 10 minutes - and they only run about every 10 minutes at that time of night. Plus deplaning and the long walks at both ends . The math just doesn't add up.

Just for reference, Heathrow's published minimum connection time for T3-T5 Int'l-Int'l transfer ON SAME TICKET is 90 minutes. That should tell you something.

Ok, so the conformance looks like the deal breaker: no matter if the plane is late, if I am not at security 35 minutes before I will *absolutely not* be allowed to board?

It is more than just 'the conformance' . . . the terminals are practically in different counties. It isn't like you are just moving to a different gate.

So even IF you didn't need to be at security 35 mins prior to the scheduled departure time and had 10 or 15 mins leeway . . . you still probably wouldn't make it.

Any reason why you didn't take the earlier BA flight from New York (dep 7:15am, arr 6:55pm), which would have allowed you to connect to the 8:40pm flight to Paris?

Yeah, I have to be on a Delta flight to London because of who's paying for it.

I think I will bite the bullet and reroute my flight, even for the hefty fee. Why aren't there flights from LHR to PAR after 8pm?

This is very simple. You won't make the Paris flight, full stop, so contact BA NOW, rebook for the following morning, pay the change fee (MUCH cheaper than a new ticket) and find someplace cheap to spend the night at Heathrow. Treat this as an expensive learning experience.

If you have to fly Delta then why not fly Delta direct to Paris?

Most traveling between London and Paris take the train nowadays, so much fewer flights between the two city. Most who take the day-time Trans-Atlantic flight to London will not connect anywhere else. And there's an hour time difference to the continent. A 8:40p flight to Paris arrives almost 11p already.

Most taking the BA flights to Paris would be connecting from one of the longhauls into London, and vast majority of those arrive in the morning or early afternoon.

Thanks for all the replies, and for why there's no later flights. I've accepted that it's physically impossible to make a T3 to T5 transfer in 1 hr, and rebooked the flight.

Thanks again!

good move...we did that transfer last week and it took exactly 100 minutes with no dawdling!