Jason,
Although Tiscali not signed up to Otelo they have signed up to CISAS, which is an arbitration service.
Apparently you need a 'deadlock letter' from Tiscali before you can go to CISAS basically confirming that agreement cannot be reached by either party but if your complaint is unresolved after 3 months you can go direct to CISAS.
Upon confronting Tiscali with this they suggested I need to write to ask for a deadlock letter (even though it is quite apparent that deadlock has been reached). They also suggested that their complaint procedure must be exhausted first. However, I am well down that road and they are outside three months, therefore I believe I can go direct to CISAS.
Unfortunately it does seem that Tiscali are prepared to lie and throw whatever obstacles they can find to avoid liability (and arbritration costs). They even told me that my line would be clear mid March but they have still left their marker on it!
Hope this might help keep the pressure on them.
Website for CISAS is www.cisas.org.uk
Regards
Mike