I've had exactly the same problem over the past couple of days - down to 256kbps from the normal 2MB service.
Using the excellent Tiscali Broadband Support forum I contacted one of the Technical staff by e-mail ([email protected]) and got an immediate response and the assurance it had been passed on immediately to the engineers for attention.
Steve also sorted out a problem I had been experiencing in not being able to logon to the Tiscali forums within the same afternoon - he kept in touch by e-mail to keep me up to date and request necessary information re username and password etc.
Any Tiscali subscribers, whether dialup or broadband users, will find that the forum support pages contain a mass of information, help and direct contact with those involved who are responsible for sorting out any problems.
Just had a very long conversation with a representative of Tiscali's senior engineering department regarding my loss of BB speed (best to date since work carried out on November 1 just under 1MB on a 2MB service).
He tried to explain to me that the line was not capable of achieving 2MB and went into various technical detail which was difficult to make out.
He advised that I should downgrad to the 512kbps to ensure a consistent BB speed...:-))
I pointed out that since April, when I first signed on for the 1MB service and then the free upgrade to 2MB, that I had been achieving the top speed (and often even better) until this week; later on in the day the speed would drop slightly but I realised the reasons with more people going online.
He informed me that there was nothing that Tiscali could do about the situation.
Furthermore he declared he could not meet my request to put the reasons in an e-mail to me as this was the responsibility of a "different" department. I suspect otherwise that this was the reason.
I now intend to contact the local exchange (I could walk there in five minutes as it's only 580 yards as the crow flies) to see what its engineering staff come up with.