Heathrow airport

Based on one experience at Heathrow I would say three hours is realistic AND take a lunch. We will go around the world the other way to avoid Heathrow. Our usual route is from Seattle to Amsterdam. If we're going to Scotland we backtrack from Amsterdam to Glasgow.

We always fly into and out of Heathrow and always arrive 3 hours ahead of departure. Sometimes we have time to kill, sometimes the lines are so long that 3 hours is just about right. I'm not sure why you would want to cheat on that time at the risk of missing your flight. Frommer's just listed the 10 worst airports worldwide and Paris' CDG made the top 5. JFK was listed as the worst. We avoid CDG and use the Eurostar or a ferry to journey from London to the Continent.

It may depend on the time of day. I usually get a flight from LHR at 10:30am. I arrive at the airport 3 hours early and always have lots of extra time. Some of the departure gates are a 20 minute hike from the terminal, so watch the departures announcements and allow time to get to the gate. There are shops, restaurants, cafes, etc. in the waiting area. I get coffee and breakfast there while waiting for my flight to be announced.

Secirity lines at Heathrow can be extremely long at times. Allow the 3 hours they suggest. No logical reason to try and play games.

3 hours ... Don't try and cheat. If you don't know the airport and it's a busy time don't push it. Everyone's in a rush so you can't push through. Even if you're on fast track it isn't always superfast and seems to depend how busy they are.

Don't cheat. Heathrow is huge. We have been there three times in the last three years. We always check-in at the three hour allotted time.

Thanks for the guidance. We will not try to make a tight connection even though it will require staying over an extra day. Oh well, we can put it to good use!