For the Brits among us, or perhaps anyone with a non-US keyboard layout, I recall when I still had my Mac, this wasn't mapped properly. It was the button on the right of the left shift. This was quite strenuous when I had to switch within the same application. I can't remember if I just re-mapped the shortcut or what it was, but I suggest you look into having that mapped to the button right above Tab (below ESC). It makes it a lot easier.