How are you using another socket? Generally the MK3 should be the only socket which syncs up.

What did the engineer say about the bridge tap? Or hadn't they told him?

I think he means what was the Master and the engineer bypassed it and fitted another.

I hope that's what was done!!!

I asked the op if that is what happened and the op said

The Master is still in the same place but he tested both sockets and the speed was the same, there's was no loss on that short cable run vs directly onto end of BT's cable.

This suggests to me that actually the engineer did not bypass it.

OP can you confirm, does your fibre connection work on more than one socket at current?

Can you take a picture of the phone socket currently in use for fibre?

If Openreach have confirmed there's nothing more that can be done you'll be told to either like it or lump it basically (keep it as is or cease with no termination charges)

I suspect that the engineer has shifted the the NTE, hence the comment about trying the speed in both locations. Doing so will have resolved the bridge tap issue.

What bothered me more was the earlier comment about being unwilling to sort something UG 'just for this line'.