In this case we managed to find the problem, not least because it also affected all the neighbours who were on the same pole. The human brain is pretty good at spotting patterns (too good perhaps, as evolutionary pressure has provided a bias towards false positives) so the connection between hearing the chainsaw start and the instant loss of broadband wasn't too hard to spot.

I did buy a spare ADSL modem a few months ago as I like to have spares for critical systems. I normally do this by replacing kit that is a few years old before it breaks. The old kit goes into storage, ready to replace a failed item. Unfortunately my new V5 Netgear DG834G has some compatibility problems with my ISP and I had to send it back. I'm rather disappointed as I've been using Netgear kit for many years without problems.