Flying ATL - FCO on Sat/Sun. I have almost 7 hours layover at Gatwick on Sunday morning. What I was going to do was try to get to Mass in Brighton (I know where the church is, have communicated with the priest, who is an acquaintance) and back. If I come in at 7:30 am and my next flight leaves at 2pm...I'm going to presume that's enough time, given my flight is on time. Is it enough time for me to go to Mass and try to get down to the beach and wave at the English Channel?

When I leave Gatwick, what's the process for getting out and getting back in? Am I going in and back through immigration?

Have you figured time post and pre flight in your 7 hours?

Yes, you will be entering the UK - so you will need to go through immigration, either tote or find a place to leave your carry-on (assuming any checked luggage is checked through to your final destination), make your way to Brighton, find your friend (and what time is this mass) and then make your way back to the airport - leaving travel time plus time for security, check in to new flight etc.

So - you may only have an hour or so in Brighton.

A local will have to tell you the best way to get from one to the other on a Sunday morning.

It looks like you'll be flying British Airways. BA uses the north terminal. The train station is located in the south terminal.

I presume your luggage will be checked through. Because you will have an international connection, you will not have to clear either Customs or Immigration. For more details, see this page: http://tinyurl.com/6f9v86.

Between Southern trains and First Capital Connect trains, you'll have at least three trains/hour to Brighton. The trip will take from 30 to 40 minutes.

you have 6.5 hours.

Count on 15 mins from touch down to entering arrivals.

15 - 30 mins for immigration. You could luck out but it mainly depends on how many other long hauls lad around the same time.

15 mins to find/use the left luggage facility. Assuming you don't want to take your carry on to Brighton. If is is small you can skip this bit - then getting to South Terminal

5-25 mins to wait for the next Brighton train. Might be an issue since weekends are when rail works are scheduled so trains can be delayed.

35 mins to Brighton/35 mins back from Brighton

Walk or taxi from/to Brighton Station -- ?? since we don't know where the church is - say 20 mins-ish

10-15 mins to retrieve your carry on and get to North terminal

60 mins advance for security/etc.

So you will use about 3.5-4 hours for just the travel/airport/Brighton logistics

If there are rail works it won't work. Otherwise, you have enough time. (Not sure I'd do it myself)

Thank you, Tim, especially. That's helpful. Yes, it's BA. So even though I'm leaving the airport, I don't have to go through immigration because I have an international destination? Someone else told me to make sure I have my boarding pass with me, as well.

Sorry, I think I need to take back what I said about not having to go through Immigration. While that would be true if you were staying airside, since you will officially enter the UK when you leave the airport to go to Brighton, I believe you will have to go through Immigration.

no "I believe" about it. You are leaving the airport and entering the UK. Of course you must clear immigration.

And you'll need your boarding pass to get through security when you return to the airport.

Update:

Mission accomplished, and smoothly, too.

Got in about 7:30 am, Sunday morning. Outbound flight to FCO scheduled for 2:05. I dithered a bit, trying to decide what to do, since I had not slept a wink on the flight over. Considered some Yotel time, noted their was a noon Mass in the airport chapel..but then eventually just decided to wake myself up by heading out into the 0 degree C weather and head to Brighton.

Took a train that left at 9:54 or so, arrived in Brighton at 10:25. The church was a walkable distance, but Mass was at 10:30, so I thought I'd cab it. Got there in plenty of time, went to Mass, chatted with the priest afterward, discussed with him and a couple of helpful parishioners whether or not I should cab it back, eventually decided to walk with a cheerful older fellow named John, who had interesting observations on the world financial crisis. We parted ways about a block away from the station, I climbed on a train scheduled for a 12:16 or so departure, was back at the airport by 12:45, and since they didn't even post a departure gate for my flight until 1:15, it was plenty of time.

(And immigration was no problem. No lines at all.)

Followed by a great week in Rome!