Best track near London, accessible by metro or train

[G]

I'd suggest you do better research to 'promote your product' - ie find an appropriate event.

Brands Hatch is probably your best bet. Snetterton isn't too far, but it's the middle of nowhere and doesn't have the Status of Brands.

However, you'd really want to think a little more about your promotion first, I'd suggest!

[MarJay]

Brands Hatch isn't really accessible from London via public transport...
____________________
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[G]

59 minutes by public transport according to google.
"In current trafffic", it'd take 56 minutes by car.
Sounds accessible to me .

Also - I would suggest this isn't akin to comercial advertising, personally.
(The other post; yes, though it was on-topic at least, even if a rather silly product that doesn't seem to provide it's design intent .)

[UnknownStuntm...]

Knockhill is pretty close by. Also look up Philip Island. HTH.