It's a really big trade volume. No-one on this forum in my opinion is trustworthy enough, at least alone to take such a transfer in one go.
As someone based in the city in London, I'm interested to know if you do manage to execute this trade successfully and how.
From an AML point of view your friend will have to be careful too... as would any seller.
I imagine I would need to use the services of a lawyer/notar to do the transaction through, but to be honest I am yet to find someone who actually has that amount of bitcoin which seems to be more the issue than how to do the transaction.....