Need tp prove adsl circuit end to end

Hi
my customer has been using adsl broadband via a us robotics 9300 router for the last two years. His isp (in the uk) is "freedom2surf.net". Since 27th april he has been unable to access the internet. He has tried telephoning, faxing and emailing his isp tech support but apart from being held in queues for thirty or more minutes he has been unable to obtain assistance.
I visited his site yesterday and took a known working netgear router and my laptop with me. I was unable to access the internet either, using his isp account. The adsl indicator is showing green ok. The routers both are accessible from any pc 192.168.1.1 and can be programmed. Just no internet access.
I need to prove that the adsl circuit is ok. Is there any test adsl isp login that I could set the router to in the uk in order to do this? If this had been a dial-up connection that had failed I would have simply set up a temporary connection to another isp to ensure that I could at least use the internet ok. Can this be done with adsl?
My customer is losing business because of this problem. No emails.

Any suggestions on proving this without speaking to isp will be most gratefully received.