On the Wii U open browser, go to either. http://ipad.tvcatchup.com or http://iphone.tvcatchup.com
Doesnt matter which you use, just whichever UI you prefer, the iphone version works best.
Signup and Login.
Click channel and watch in glorious HD too.
This works as it's a HTML5 stream, and should work with any ipad/iphone compatible streaming web sites, I'm sure you can think of many.