Dunno where you're getting this from, Adam, but you've been misled.
Meantime London Porter[/url:1wsv1b6p] is the historical 6.5% ABV one. It's very very nice, but isn't 100% brown malt.
Meantime London Stout[/url:1wsv1b6p] is 5.4% ABV and is quite a dry, earthy sort of beer. I quite liked it, but opinion is divided. It's not 100% brown malt either -- black malt is in the driving seat here.
I've seen both in Dublin's good beer offies fairly recently.