This might be a good place to start.Different London Porter
They attempted to clone the beer on CYBI on The Brewing Network Friday. I have not listened to the show yet, but it should point you in the right direction.
The recipe Blatz posted above (that I posted at NB after quoting it from an English board. Ain't the Internets great ?) will get you very close. I'll have to check out the BYO article, though.