In article , Roland Perry
writes

All in all I'd reckon you can only make this transfer by taxi, and even
then there's a more than 50:50 chance that you'll miss the Heathrow
flight. Perhaps you can find a taxi firm and call them from the USA
departure lounge to arrange the pickup. That way, if the plane looks
like being significantly delayed you aren't wasting your money.
--

I'm with Roland and Mike - book Mike and his taxi. A guaranteed ride
which will be waiting for you the moment you clear immigration and
customs. dedicated run and Mike knows the alternative routes if the M25
is clogged (there are major roadworks on the M25 between the M3 and
Heathrow at the moment).

You are against the clock, change your connecting flight or use Mike.
--
Andrew
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