Hello:

I am going to be landing at Heathrow Terminal 3 (American Airlines) and taking off from Terminal 1 (BMI). Is an hour-and-a-half enough time to make my connecting flight? What is the absolute minimum?

NO!

If your plane is on time or early, you are in first or business class and can get out of the door in a hurry, you have only lightweight carry-on luggage, are a fast walker or long distance runner, there is a transfer bus waiting to leave when you get down the stairs, there is virtually no line at security, AND you are not selected for secondary screening, you might make it.

The minimum legal connection at LHR is two hours. The minimum connection for checked luggage is 4 hours.

I am uncomfortable with anything less than 3 hours, even though I avoid checked luggage and am skilled at avoiding luggage searches.

Thanks Jeff! Your help has been invaluable! I was deciding between a layover of 1 1/2 hours or 4 hours. I would have decided unwisely.

No - minimum time at Heathrow is 120 minutes - and per my latest experiences that is cuting it VERY tight. I wouldn;t be comfortable with anything less than 2.5 hours (assuming carry-ons only) - more if the flights are on different tickets.

Having just been at Heathrow this morning, and having been slowed down by every possible airport glitch you could imagine, definitely do not give yourself less than 2 hours. And I agree with NYTraveler--that is cutting it tight. And FYI: Terminal 4 was terrible--and I was told that was the best of all the terminals! Yikes!