Ok, I thought this would be easier to explain in diagram form, so this was the setup with ADSL until this morning:
When the engineer came, I explained that I couldn't have the modem and hub at the existing master socket, and he agreed to move the master socket to the existing internal extension,m making the master socket a blanking plate (as it was never used anyway) and simply joining the wires behind.
Except that the existing wiring didn't go straight from the master socket to the extension, it went via the monitored burglar alarm first, which was connected by microfilter (provided by the alarm company). I told the engineer about the alarm, but he said he didn't think it would be a problem.
After an hour or so, the setup looks like this:
The infinity works great, speed and stability are perfect. Except neither the phone or the alarm get a dial tone. I suspect this is because the alarm is now connected "behind" the master socket (ie: before the filter).
Would this be right? If yes, what would need to be done? Will I have to get the BT engineer out again?