We are flying out of Heathrow on Sat. Dec. 23rd at 7am to go to Rome. As Americans do we have to do all of the immigration stuff to go . . .and do we really need to be at the airport at 4:00am?

Not quite sure what you mean by &quot;<i>As Americans do we have to do all of the immigration stuff to go . . .</i>&quot;

Do you think only some nationalities go through security/passport control??? You don't go through immigration at your departure airport - but at your arrival point (immigration is entering, not exiting)

You will have security (more than once) and check in/passport control. That is a very busy travel day so you will want to be at LHR early - but 0400 may be overkill. I'd want to be there by 0500 for though.

janisj is spot on

I was just at Heathrow a couple of days ago. The line through security was long. It might take about half an hour to get through security. Please note that they strictly enforced the one bag rule no matter what.

It was reported elsewhere that some people took two hours to get through security at Terminal 4 yesterday and it won't get any quicker as Christmas approaches so it really is important to be there in good time.
I believe the marquees are up again!

As other posted, it's not immigration but the security check queue that will take the most time.
You surely will be travelling at a busy time. It would take less time if you're travelling only with hand luggage, or check-in on-line and do a fast bag drop if you're flying BA. On the other hand, if you're flying Alitalia with luggage to check--you will need to get there early as they have only 2-3 counters and the queues are really slow-moving.

According to news reports today, marquees have now been erected at Heathrow due to overcrowding in the main terminals. Queues are horrendous. It looks really mad and busy, and it is expected to last through to January. To be on the safe side I think I'd try and get there 3 hrs before.
There's every liklihood that the airport roads will be clogged too with that many people at the airport.

re-thinking what I posted -- the reason I said 0500 was because normally for the first flights of the day the queues are not as slow and not much is open at LHR (including check-in desks) that early.

But considering the HEAVY travel day next Saturday, 3 hours is probably prudent.

so yes, 0400 or soon therafter . . . . .