Just as a general comment, you'll be better off on British forums if you're asking about the recipe of a British beer, being US-based most HBTers will barely have heard of Magic Rock, let alone drunk the beer.
GP is the posh barley variety of the north, used in a lot of Scottish whisky and by brewers like Tim Taylor. It's a bit sweeter and less biscuity than Otter, but they occupy similar positions as the premium barley of their regions. So if you've got Otter then use the Otter, otherwise GP is easy enough to buy here.
London Ale II yeast (another site says London Fog ale yeast)
Wyeast 1318 London Ale III and White Labs WLP066 London Fog are roughly equivalent, they're the standard choices of yeast for modern-style hazy beers. Lallemand Verdant is a dry yeast derived from 1318 so is a convenient alternative if you're not into liquid yeasts.
It looks like they've messed around with the recipe a fair bit, as Magic Rock have two pages for the beer -
an old one that has :
Malt : Acidulated, Dextrin, Golden Promise, Oat
Hops : Amarillo Lupulin Powder, Citra Lupulin Powder, Ekuanot Cryo, Mosaic Lupulin Powder
Yeast : London Fog
and
a new one that glosses over the malt bill (which makes me think that the Lion/Kirin accountants have insisted on something more economical than GP to hit the supermarket price points), and doesn't mention yeast either.
Tesco lists barley and oats as allegens, some like
Beer Merchants add rye as well.
Bravado started out with the original Saucery grist and added rye for body, and fermented with " London Ale II" (surely they mean London Ale III?) in the blurb. But then the "brewsheet" table bears little resemblance to that blurb, with no mention of rye, hops in LUPULN2 and T90 format and saying the yeast is WLP002 in the table (let's say that would be an unusual choice for the style) .
If nothing else, the proof-checking of the website is appalling. But my guess is that Bravado was essentially a testbed for changes to Saucery. I suspect they've changed from White Labs (ie London Fog) to Wyeast (London Ale III), they've replaced some or all of the GP with a cheaper base malt plus some rye, and gone over to cryo for most of the hops.
