Has anyone managed a day tour of London while on layover? Not traveling with guns. How much time is the minimum if you did?

I’ve done it several times when my layover was 9+ hours. Catch the express train from Heathrow to Paddington station IIRC and exit in the heart of London. Easy walk to many interesting sights.

How much time do you have? I’ve done it many times, but with long layovers. With a 4-6 hour layover, I would suggest you head to Windsor instead. Easiest way to exit T5 and head to the Sofitel and order an Uber to pick you up.

More time you can take the Heathrow Express to Paddington as stated above. It’s a bit pricey but faster then the tube.

We have 7 hours.

That’s a bit tight since you have to clear customs into the UK and clear customs again outbound plus airport security. The trip into London will take at least 45 minutes each way, not leaving much time for sightseeing. My advice would be to stay at the airport.

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7 hours - even with boarding cards in hand you will need to be back at Heathrow 2 hours before departure - leave 5 hours. Into town and back 90 mins min leave you 3 h 30 mins ..... you could maybe take in 1 max 2 sights or have a nice meal and head back to Heathrow. Pretty tight ....

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Go outside the airport and find a black cab. Give the guy a couple hundred dollars and he will take you all over the city.

Take the TUBES to Piccadilly Circus. Grab a quick bite to eat at Brasserie Zedel, a Michelin Bib Gourmand restaurant only 100 yards from the Tubes stop. They have a prix fixe 3 course meal there for less than $15 US. From there, walk about 200 yards toward the large KFC sign where you can pick up the Big Blue Bus to tour the city. A complete circuit lasts less than 2 hours and you can hop on and off as frequently as you wish. Bring your IPHONE to take pics of Big Ben, Parliament, Buckingham Palace, the Shard, etc. I always stop at the Duty Free shop at Heathrow and buy some Cuban cigars and when my butt gets sore from sitting on the bus, I hop off the bus and fire up a Montecristo. I head back to the Tubes at least 3 hours before my next flight.