"Earl Purple" wrote:
left onto A4201 (Albany Street) (just after Regents Park, which you can
go through as an alternative). Follow the road round into Parkway and
at Britannia Junction (Camden Town) take A503 Camden Road and follow
this road all the way to Walthamstow.

yes, don't rule out this option - at that time of day, this will be a
crawl
lasting hours but may be a bit more predictable than the circular routes
(i.e. there's less risk of getting completely stuck).

The tube is more predictable, less stressful and will take half the time
compared to driving, whatever route you choose, but I guess there's a
special reason why you need to drive.

you can also cut out a bit more of Marylebone Road by turning left into
Lisson Grove (2nd traffic light after the flyover) or even into the
first one (is it Bell Street?) and then rigth to get onto Lisson Grove.
Then right at the 2nd traffic light (St John's Wood Road), past the A41
and along Prince Albert Road then left into Parkway and as before.

But if they're leaving Heathrow at 3:30pm, they'll be getting to Marylebone
around 4-4:30-ish, and the inbound flow on the A40 is actually very good -
the issues won't start until coming away from Camden on the A503.

--
"For want of the price of tea and a slice, the old man died."