What I'd probably do is first check to see if you can connect through a PC or MAC to his slingbox. If that's successful and you can connect to his slingbox using your browser, hold the ctrl key on your keyboard and click on the video that's playing. Check the stream statistics to see if you've got a TCP stream running and not a SNATT stream. You might have a connection issue due to the stream type being sent to the slingcatcher. If you can't connect due to a SNATT stream, ask him to check the port forward settings on his router in London and get him to verify the sling setup to make sure it's not reverted back to automatic port forwarding and has been setup using manual port forwarding. If the problem is stream related, a TCP stream is what you need for a slingcatcher to connect to a slingbox. Anything else showing up will point to the problem. Not much you can do on your end if the update to the slingbox has wiped out the remote viewing settings. Just ask him to check that everything is correct and if it is, get him to do a reboot of his modem / router and slingbox and try it again.
That's the first thing I'd try. Check the U.K slingbox and router remote viewing settings.