The problem seems to be due to capacity issues on the Tiscali peering network, where they peer with other ISPs in the UK. Customers who have direct connections to Tiscali do not seem to be affected.

We have raised a ticket with TeliaSonera to try and get them to put pressure on Tiscali to fix their problem.

We have a direct connection to Tiscali already signed up, however we are waiting for the fibre cable to be laid in Telehouse London, which I hope will be done next week, however its difficult to get an accurate time from them.

In the meantime on Monday evening we are going to try and move outbound Tiscali/Pipex traffic to another carrier to see if this fixes it.

Hope this may help you and your customers!