My account is not valid for use in the uk store. What does that mean and why can't I update my aps now?

Welcome to the Apple Support Communities

It means that you created an Apple ID on another country, so you have to use your Apple ID with the store of the country where you created the Apple ID. Go to Featured tab, scroll down, press the flag at the bottom right and choose the country where you created the Apple ID, so you will be able to purchase applications and update the apps

You are welcome

The same problem occurred to me after updating the iOS yesterday (Feb 6th 2013) - i guess its a glitch yet to be spotted & ironed out by Apple...

Here's what fixed it for me:

On your iPad go to Settings > iTunes & App Store > click on your apple ID > click on View Apple ID > click on your country / flag > selct Change Country or Region > reselect your existing country > agree to terms & conditions (after reading all 33 pages of them...joke) > ignore payment details and click Next. That's it. Now try to update apps and download as usual.

Best of luck