Feign madness.

Rats! He's American, and thinks all Brits are crazy anyway. In your case, he does seem to have a point...

He limps towards you, the sound made by his awkward gait contrasting with that of two people running towards you from the direction of the escalator.

"Please - take this", he says, proffering the package. It looks to be a painting wrapped in brown paper.

At that moment, you notice the rush of freezing air that signals the approach of a train.

You can:

Get on the train the instant it arrives, ignoring the man.

Grudgingly accept the painting and board the train.

Wait a moment to see who's running round the corner. Well it could be the police!

Tell the man to stop bothering you.