This was the suggestion made by technical support for Tiscali when I spoke to them this afternoon to report a slowdown in our service.

You need to turn off the firewall setting on your router.

The initial explanation for the crazily slow speed was that it was peak time. Once I answered that, then it was time to reduce our security! Or not.
Yes, Tiscali may be cheap but their customer service experience constantly redefines the horrors of offshore outsourcing.
The final solution offered was that we upgrade our service from 1M to something faster, which given that at the time we were getting somewhere in the region of 10Kbps through the line I found to nicely sum up the call.

The line did return to normal shortly after the call. Maybe the 5th reboot of the router was the charm? Maybe the Tiscali line test changed something? Or maybe that butterfly flapped it’s wings again?