So do we have ample time to see London.

First of all, I would definitely book a hotel by the airport. You will really need the sleep after your flight from Phoenix. It shouldn't be hard to go to bed early, which will give you a nice long sleep, even with an early flight. That will leave very little time to do anything that day, but if you find you feel okay after you check into your hotel, you might have time for a very short trip into London, or Windsor, which is closer. I would forget about the hop on hop off bus. You won't have enough time to make it worth the cost, and you may fall asleep if you don't stay on your feet and keep moving.

No you don't have have "ample time" to see London but you can take a peek from a HoHo bus in the evening and get a bite to eat before you return to the airport for your rrrrrrealy early flight the next morning.

I think in your situation I would spring for a hotel IN the airport for your flight. If you figure out which terminal you'll fly out of and look at a map to see which terminals have hotels, then book a room in that terminal's hotel. If you do this you can store your luggage at this hotel while you explore London on your late afternoon/evening time.

EDIT: their are only 2 terminals that have hotels. Terminal 4 has a Hilton and terminal 5 has a Sofitel, budget accordingly.

Please check to see what time the hop on hop off tour ends for the day. I seem to remember it did not run in the evening when I did it, but it's been a long time since then.

Given the early morning departure I would also suggest that you stay at the airport.

If your flight arrives on time you would have just enough time to do a quick tour of one sight (National Gallery, British Museum, British Library) and grab a quick meal.

London tube will get you in and out of central London cheaply but will take about an hour. Heathrow express is faster but will cost more, discounts if you book in advance.

No, no, no. Look - under the best of circumstances, you could be at a hotel by 3.30. I would grab a hotel close by and maybe hop the tube to Victoria station (one change unfortunately and an hour trip) and walk a couple of blocks to the Buckingham Palace and wonder through the park for an hour or so. Find a pub in the Victoria station area, grab a sandwich and head back to your hotel. With a 6.20am departure you will need to be in the airport by 5am. Good luck. By the way, who booked this schedule? I would fire them.

As others have said, not much time, book a hotel near the airport, easier to get back there at night than in the wee hours of the morning. It is not a bad idea though to head into London for a walk, depending on the location of your hotel (you land, get through immigration, find transport to your hotel, then transport into London, suprised if you would get there before 5:00 pm.) but as a suggestion, I would head to Westminster station, that will take you into the shadow of Big Ben, wander near Parliment, over to Westminster, then up Whitehall (10 Downing, monuments) and into Trafalgar Square. from there, find a place to eat or drop into a pub for an ale (Covent Garden and SoHo are nearby) then head down to the Thames for a walk one way or the other before hitting a station to take you back to your hotel.

You don't say when, so it's difficult to tell what the weather or daylight will be light.

The bus tours can be really, really slow due to traffic so I wouldn't bother.

Get the tube to Westminster station, marvel at Big Ben & Westminster Abbey from the outside, walk across the bridge towards the London Eye, walk east along the South Bank till you get to the Globe - and St Paul's Cathedral across the river.

Grab something to eat on your travels.

Then get the tube back to Heathrow and check into your hotel for the night.

I would go into Windsor, its only a 15 minute taxi ride from Heathrow. You can tour the castle, walk to Eton and see Elton College, which isn't really a college its a middle school/high school where aristocrats and royal families send their boys to. Great pubs there to have a good pub meal.

oooh now THAT sounds like a great idea, Robin!! Very clever, much easier on the exhausted jet-lagged body, and gives a nice olde Englande feel, too, I bet.

You will probably be severely jet-lagged. Consider some of the tips here but for sure,you need to stay near Heathrow overnight.

Just a quick observation - but if you stay near and not at the airport, and planned on taking the airport hopper bus - how early do the buses start (? - maybe someone knows) - may have to arrange a taxi...

When I've had a similar situation all I've had time for was to head into the city for an early dinner and a pint at a pub then back to the airport to catch some rest before catching my early flight.

DJ

Some more info, courtesy of TA:
https://www.tripadvisor.co.uk/Travel-g186338-c195392/London:United-Kingdom:Heathrow.Layover.Central.London.html

Thank you everyone! Great to have help. I knew we were crazy to book this way (it was me) but as it was frequent flier miles I was feeling stingy & wanting to use minimal amount of miles. So, I thought perhaps a quick trip into London was feasible. Certainly wouldn't expect to see much but.... So we are staying right at the airport and depending on jet lag will try to venture out and see something. At least we can communicate and ask questions without too much difficulty! Thank you! This forum is awesome.
Have traveled with Rick since 2003. (Though not as frequent as I would like)