The only problem that may occur, is if the fault is after the master socket on any cabling or sockets that you have provided.BT will make a charge for this. If all the sockets and cabling were provided by BT as per their rental service agreement, then there should be no charge.
The mastersocket and the 2 other extensions (3 in total) were put in by BT orginally. Should all 3 socket then receive a working broadband signal ? ie If they have to re-wire inside the house, will this be done for free or can they charge for this. I know if it was a DIY extension they would, but if put in by BT what do you think ?
If BT installed the system, and are making a rental/service charge, then there should be no charge for any work that they do, unless of course, you have intentionally damaged the system.You should receive broadband on all sockets, but remember that a filter, which may have been supplied by you or the ISP may have a fault, and it is worth considering this, as this could validate a claim against you. If the fault is with their system and they try to charge, then make a complaint.
I had a similar problem when i moved house.I had no signal and tried four different filters. My ISP said that there was nothing wrong with their broadband. After approx two hours in total of talking to a numpty in a foreign land they eventually agreed to get BT to look at the line. My phone worked but there was no ADSL. The engineer did something to a box on the BT side of the master socket and hey presto ADSL. The only down side is that BT tried to charge me £150 for this.(has since been sorted). If you cannot see ADSL activity on your modem then it is probably BT/Tiscalli fault.
Just in case they try to charge, I would argue that it is a rented line with all extension installed by BT, therefore it is their responsibility to make sure the line I rent is working properly for broadband and their responsibility to fix it that a working adsl signal is supplied to all extensions.
Is there anything else I should mention, or anyone I should contact (only if they try to charge)
Personally, I wouldn't mention anything at present. You have stated that Tiscali says 'there is a line fault', and they have made arrangements for BT to deal with the problem.Leave it at that for the time being.
Have BT or Tiscali informed you yet, of an appointment date of engineers attendance!.
If there is a mention of a charge at a later stage, then take up any complaint from there.