Thanks! The process / relationships between the CPs and the infra provider and its sub-contractors does , unfortunately, seem to lend itself to evasion of responsibility, and though it may not be specifically by design, outfits like M J Quinn will cynically take advantage.
Thank-you once again for most helpful comments.
The way these things should work , if the contractor is reluctant to accept responsibility, you complain to PN , they complain to OR about reputational damage, OR complain to Quinns about the same thing , eventually they concede, it’s a pain that these things need perseverance considering Quinns no doubt have insurance for these things anyway, (although it’s also true some consumers will try it on and make ludicrous claims ) what you can’t do is complain directly to OR , you are not an OR customer, and to labour the point BT have no involvement whatsoever, making posting here here somewhat pointless.
The OP has did not have contract with Quinns. He did not pay them anything or ask them to do any work nor did he have a contract with Openreach he also never asked them or paid them anything to do any work.
Openreach who sub contracted to Quinns only did the work because PlusNet contracted Openreach to do the work and ultimately will pay them for the installation.
It is solely the responsibility of PlusNet who is the company that the OP took out a broadband package with which included the installation who should compensate the OP because it was their contractor that messed up.
Openreach and Quinns can fight it out with PlusNet whether or not they will compensate PlusNet for any compensation that PlusNet is required to pay the OP because of the damage that the installation contractor caused.
As for Openreach and Quinns trying to pass the buck it does not matter a jot. The OP should never have been in this position. He should have been told by Openreach/Quinns to lodge a complaint with PlusNet who will deal with the matter.
The OP will no doubt have to submit a claim for compensation and proof of what has been damaged. He obviously can not prove that the damage was caused by the contractor but the balance of probability, which is what would be used in a civil court case such as the Small Claims Court would most probably find in his favour.