Is Heathrow or Gatwick better with a short layover window?

If I understand correctly, you are flying Paris to London on one ticket ( with checked bags) and then on to Iceland on a separate ticket, and want to know which London airport gives you the better chance of being successful with a 2.5 hr time frame?

To paraphrase Kipling, You're a braver man than I am, khanck

I have not tried the type of transfer you are describing. I do know that I have waited an entire hour for my suitcase to show up at baggage claim before at Heathrow. I’ve also had it there in 20 minutes. The challenge is you don’t know in advance which wait time it will be.

My guess is that Gatwick might be a better choice because even if you had to go between the North and South terminals, it is just a few minute direct ride on the rail system there.,

With Gatwick the check in and bag drop is all very hectic and security can be fairly long but it is a smaller airport, easy to get around and transfer between the two terminals is very quick via the rail shuttle.

Heathrow just seems to be more organised in terms of check in and security so it beats Gatwick in that respect however it is larger and takes longer to transfer between terminals.

There are pros and cons to both airports but nothing strong enough to persuade me towards a particular one.

If you're able to change your flight from Heathrow to Gatwick, can't you change it to a flight from Paris? That sounds like the easiest way to solve the problem.

3 hours for a self transfer at Heathrow sounds too risky for me. If it was my trip, I'd take the train to London and spend the a night there if I couldn't change the flight to Paris.

The general advice on changing at Heathrow on separate tickets is that you should allow at least 4 hours and I can't really see that I would recommend much less for Gatwick. Whilst Gatwick is a smaller airport than Heathrow it's not small - around the same size as Boston and Houston in passenger numbers.

I have gone through both airports a number of times and Gatwick seemed to always have the longer lines especially at Passport Control.

If you have a US passport, you will be able to use the egates.

But I'm with Badger, why not see how much it will cost to fly from Paris to Reykjavik. You might be surprised.

As you have already booked and i presume paid for that ticket for your fight from LHR to REK, you need to stick with LHR unless your ticket is changeable or refundable without a fee. Or you wish to incur the fee(s). Whether you are using LGW or LHR, you need to think about arriving in London the night before and staying in London. Nothing like your flight from Paris being delayed or cancelled and you miss your flight to REK to turn your plan totally upside down.

If you will give us your itinerary someone on these boards will come up a thought or two to help.

Thanks all! It sounds like 2.5 hour transfer is a bad idea so will focus on plan B. I appreciate the suggestion to change the flight to Paris to Keflavik direct -- I originally thought I couldn't do this since the original flight is a round trip with stop-over flight on Icelandair (London - Keflavik - Seattle) and they don't let you do both multi-city and stop-over on the website. Probably worth a call to customer service though to see if they can change it manually. Thank you for the advice!

I'm not up to date with Icelandair's ticket rules, and it probably depends on what kind of ticket you have. But if you can't change the ticket to Paris, you probably can't change it to Gatwick either. But you can always ask them.