Ok, here's the original:
7 lbs Pale Malt, Maris Otter (3.0 SRM) Grain 63.64 %
1 lbs Oats, Flaked (1.0 SRM) Grain 9.09 %
12.0 oz Victory Malt (25.0 SRM) Grain 6.82 %
10.0 oz Chocolate malt (pale) (200.0 SRM) Grain 5.68 %
8.0 oz Barley, Flaked (1.7 SRM) Grain 4.55 %
8.0 oz Black Barley (Stout) (500.0 SRM) Grain 4.55 %
8.0 oz Caramel/Crystal Malt - 80L (80.0 SRM) Grain 4.55 %
2.0 oz Chocolate Malt (450.0 SRM) Grain 1.14 %
2.00 oz Williamette [4.80 %] (60 min) Hops 31.6 IBU
1 Pkgs British Ale II (Wyeast Labs #1335)
Maris Otter doesn't come in an extract, so you'd have to sub either liquid extract or dry extract. It won't be exactly the same as fully maris otter, but it'd be ok. You'll need to mash more grain that usual, because the oats need to be mashed with some base grain. Hopefully, you can mash 6 pounds of grain? You'd need a very large grain bag, or two or three small ones.
For the grains:
2 pounds maris otter
1 lbs Oats, Flaked
12.0 oz Victory Malt (25.0 SRM)
10.0 oz Chocolate malt (pale)
8.0 oz Barley, Flaked (1.7 SRM)
8.0 oz Black Barley (Stout) (500.0 SRM)
8.0 oz Caramel/Crystal Malt - 80L (80.0 SRM)
2.0 oz Chocolate Malt (450.0 SRM)
Bring 9 quarts of water to 169 degrees, in a large pot. If you have room, add the grain bag(s) with the grain to this pot. If not, you can use a cooler/bottling bucket/whatever. Stir well, to thoroughly wet the grains and make sure it's between 152-158 degrees. Cover, insulate with a blanket or something and let sit for an hour. After an hour, drain the liquid from the grains. You should have about 1.5 gallons of liquid. Pour hot water over the grain bags, up to your boil volume. Ideally, you'd have room for 2 more gallons or so. Stir well, and drain again. Add that to the liquid you already have and bring that to a boil.
Once boiling add the hops as in the original recipe.
At 10 minutes left in the boil, take off the heat and add a can of Alexanders pale malt extract (4 pounds liquid) and stir well. Or you can add 3 pounds light dry extract. Both will work. Stir well, bring back to a boil, and boil 5 minutes. Take off the heat and cool. Top up to 5 gallons.