The affected router is back in service and helping stabilise the network.
Investigations show that although the router had "frozen", it was still doing various operations, but doing them very badly. This obviously had a major impact on the rest of the network.
We will be monitoring the London network very closely. These routers are to be replaced during the scheduled maintenance on Monday night (2nd December):http://status.surevoip.co.uk/incidents/npzhmmlnzp68
Thank you for your patience and sincere apologies for the interruptions to your business and customers.
Gavin and the SureVoIP Team.