I wanted to land in Heathrow early in am (6 - 7) and make it to Luton for a flight to Sardinia leaving around 11 am. I'm beginning to think, based on what I've read in the forum, that this may not be feasible.
Does anyone have any experience with this? (Luton is the only airport I can find that has flights directly to Sardinia from London.)
Any other ideas?
Thanks.

I would not try that transfer w/ less than 6 full hours. and that would be cutting it too close for my comfort.

I think you can fly to Olbia from Gatwick. That might give you more choices than just easyJet out of Luton

If you did insist on going from Heathrow to Luton, I think this is the best plan:
Tube to Kings Cross/St. Pancras
Train from St. Pancras to Luton
Shuttle bus (free) from Luton to Luton Airport - a 5-minute affair

I'd expect this all to take about three hours if starting from the tube station at Heathrow, having purchased my tube ticket (but not the train ticket). I don't recall it being difficult to buy the train ticket to Luton, but it does take a bit of time, and you'd have to connect to this train.

So since you'd want to be at the Luton airport two hours in advance, and actually landing, getting luggage, going through immigration, and getting to the Heathrow tube station can all be lengthy proceedings, I similarly agree that five to six hours simply is not enough time.

Thanks for the info. I take it from what you're saying that there isn't some direct shuttle bus or equivalent directly from Heathrow to Luton?

Yes, there is a National Express coach. But it take roads that will be very congested during the morning commute. The coach runs approx once an hour so w/ a 0700-ish arrival even if you could catch the 08:10, you wouldn't get to Luton intil 09:20 or later - possibly much later.

If you caught the more likely 09:05 coach, you would not get to Luton until 10:15 at the earliest, which is too late.

If you've already booked, you MIGHT save the situation this way:

Heathrow Express To Paddington
Tube: Bakerloo to Oxford Circus, follow signs for NORTHBOUND Victoria Line, Victoria Line to Kings Cross
Exit following signs to St Pancras. First Capital Connect to Luton Airport Parkway
Bus to terminal

Between 0700 and 1000, this is the fastest, most reliable route. Maybe uncomfortable, but it'll get you from the station at Heathrow to the station at Luton in under 90 mins.

Still wouldn't do it if I didn't have to, though

That doesn't sound too pleasant. I wonder if I could hire a service to drive me there? I assume they exist, but are probably pretty pricey. Does anyone know? Thanks.

A car has to take the same roads as the coach - it would only be marginally faster. Look at a map - Luton is 60 miles from Heathrow.