Incredibly slow Mac App Store downloads

I'm trying to download Empire: Total War on my new MBA 1.7 i7/8gb ram. It's got 445gb of free space and it's less than two weeks old.

It's lightning fast, except when trying to download Empire: Total War from the Mac App Store.

It's been downloading for two hours and it's managed a total of 2.9MB of 13.8GB. At that rate it will take nearly a year to download.

I've run speedtest.net and my DL is a consistent 25mbps and it streams from netflix in HD no problem so it's not my wifi or my internet connection.

Any ideas?! I'm tearing my hair out!

Thanks