peter wrote:
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

Northfields trains also don't serve Heathrow.

And Piccadilly Line trains sometimes change their destinations during the
journey, typically at Acton Town, so it's worth paying attention to
announcements and the electronic displays. It may be best to simply take
the first train to leave Cockfosters, and change if necessary at Acton
Town, as other Heathrow trains will have commenced their journey further
west along the line (not all eastbound trains go as far as Cockfosters).