Yes, it is. Stick to cups and spoons like a good American.
Hahahaha! I am all about the cups and spoons, but I keep an open mind. If the recipe is given in grams and mls, I'll do it that way.

I wonder if your recipie accounted for the higher water content of margarine that that is why the butter isn't working... *shrug*
The recipe called for butter. It's an American recipe from Tollhouse...one that I've long considered tried and true.
US 'all-purpose' flour and UK 'plain' flour are slightly different - I think it has something to do with the gluten content/percentage. 
Thanks for all those links (and the other ones further down)! This is more involved than I thought.

I used the Dr. Oetker baking powder we bought at Asda and everything turned out just the same as in the US. I didn't bake cookies with it though. I used it in cornbread and pancakes and they puffed up just the same as always.
That's funny because I use Dr. Oetker, too, and everything else I bake
does come out just as it did in the U.S. I regularly bake banana bread and have been known to try my hand at other muffins and quick breads, as well. No problems at all there! It's just the cookies that are baffling me, which is why I was so stumped!
***
Thanks to everyone who chimed in with helpful suggestions. There's a batch with your name on it when I get my cookie-baking back on track. Maybe I'll bring some to the meet-up in August!
