So I found this advice on another site and wondered about it. Is resetting the network settings dangerous? I am quite new to all this sort of stuff and don't want to bust my iPhone on day 1!
That didn't work for me...
But this did from: http://support.apple.com/kb/TS1398
In some cases you may need to reset the network settings for your device. To do this, choose Settings > General > Reset > Reset Network Settings.
Then I turned of all WPA on my router, connected - it got an IP!
So turned WPA back on reconnected and wireless is still working!