Can't connect to internet via Sky Broadband WiFi or Ethernet

My MacBook Pro has recently stopped connecting to the internet via my Sky Broadband connection using either the wifi or direct ethernet cable connection. This has happened both at my home and my son's house (also Sky Broadband.)

If I boot the MBP to Windows the connection works.
Connection via 3G USB modem works.
Connection at work, via their LAN, using both cable and wifi works.

Two other Mac's and my iPhone work quite happily on the wireless connection.
This tells me that the problem is specific to the systems settings on the OSX side of my MBP, not the Airport modem nor the Sky Broadband router.

I have set the TCP/IP settings for DHCP but this results in a self-assigned IP address on both Airport and Ethernet. I have tried to set this manually (avoiding the addresses of the other devices on the network) but still no success in connecting. Airport 'sees' the Sky box but will not connect to the internet through it.

I have tried setting up a new location with new settings -
tried deleting the Airport listing in Network Pref's and adding it again -
tried taking the 'SystemConfiguration' folder out of Library/Preferences and rebooting the MBP to generate a clean set of Pref's.
Prior to trying all of this I had restored the whole system from Time Machine to a date when I knew everything was working well.

So, I have now run out of ideas and come cap in hand to the great font of all knowledge that is the Apple Discussions Forum....... Don't let me down, boys and girls!

Message was edited by: Bob Bridges1