I love Safale 05, but I don't think it's really the proper yeast for an English ale. It's really going to ferment out pretty dry. How big is your "big english ale" going to be? Depending on what you want your final gravity to be, you might consider using Safale 04 as a more fitting yeast for an English ale.
I do think that S-05 is similar in attenuation to Nottingham. They have both fermented my beers to under 1.008 regularly.
I would definitely use S-04. You might get slightly less attenuation and slightly more English yeast flavors, but it's probably the best dry yeast to replace Nottingham with in an English ale.
Nottingham's a damned good yeast, though- and it shouldn't be very hard to find- in fact, sometimes its the only yeast i can get around here, but they've always got HUNDREDS of packets of Notty available at my LHBS (all three LHBS's, actually)