American 2-row will make you a perfectly fine beer, even for this recipe. If that's all you can get your hands on right now, go for it.
But as the others have stated, Maris Otter (or other UK 2-row) would be a better choice, if you can get your hands on it. I would ask the LHBS staff if they can start stocking Maris Otter. A LHBS that does not stock MO is not a LHBS that I would continue frequenting for much longer. It's such a staple grain for brewing that I can't imagine why they wouldn't.
Edit: or as chickypad hinted at, maybe the guy working the counter at the HBS is a dummy and doesn't realize Maris Otter and Golden Promise et al ARE varieties of UK 2-row, and they do have them in stock. I've had similar things happen to me before....