We arrived back, and our wondertenant, Stu, said that the wireless ADSL gateway had been playing up, and for the last month or so, had been declining everything but dull old port 80. So I logged onto http://www.eclipse.net.uk's ticketing system to find this:
There appears to be an unsecured wireless ADSL gateway running on the above IP address. There is no WEP in use, and we are able to connect to the gateway and browse the web via the gateway. This was discovered during a routine wireless sweep of our own network. The signal is weak but reliable at Old Street, in central London. Subsequently your account has been placed in a restricted configuration to prevent further abuse. Please secure the gateway using WEP so that only authorised access is allowed.
Please contact Technical Support when you have cleared the issue so the restrictions can be lifted.
If a personal wardriving visit from your sysadmin to check that your network is secure isn't customer service, I don't know what is.
stef