Bloody Americans... What do they know about critiquing British copy?
Actually, Rachael gave you some good stuff if you are writing to Americans, but you did say your target is for the Brits, right?
If I were you, I would contact some British copywriters for this one.
Reason being is that there is a big difference in the way Brits speak English versus the way Americans do.
One of the big things that gives away who is and isn't a spy is not the words they use, so much. It's the way they USE those words in a conversation.
It's not just slang, or just being able to understand cultural humor.
It is the tiniest of things that are a dead give aways to either being real or an impostor.
I could give you some pointers on how I rank your page as far as looks and formatting goes, but you didn't ask for this.
Like I said, look around the board and PM/contact some of the British/U.K. copywriters.
If it were me, I would try to contact the orange man for a couple of tips (if he's not too busy).
If nothing else, you could always go with some Aussies to help you through.
Try PMing the Cartoonman and see if he can give you a little probono help as well.