On Tuesday, January 20, 2015 at 3:37:02 AM UTC, weeyin wrote:
I'm driving my son and his family down to London late afternoon via M11
or A1 and they need to get to Heathrow. I thought it might be easier to
get them to a tube station with a direct journey into Heathrow. Any
suggestions which one you care to offer will be really appreciated or
alternative ideas

If you're coming down the A1(M) then one option is to join the clockwise M25 at J1, leave at the next junction (J24) and take the southbound A111 to Cockfosters, about 2.5 miles from the motorway. There is a (paying) car park at Cockfosters tube station (although if it's before about six on Monday to Friday it may be full), and a bus-stop lay-by directly outside, and frequent tube trains to Heathrow.

It's a tedious journey, though, Cockfosters to Heathrow. Allow a good 90 minutes, may be safer to say two hours, and check which terminal you need. Trains serve either T4, followed after a long wait in the platform by T123, or T123 then T5. Some trains do not serve Heathrow at all - these will probably be displayed as 'Rayners Lane' or 'Uxbridge'. Obviously you'll get a seat at Cockfosters, but the train will probably become very crowded through central London

Good luck!

Peter