I got and fitted one of these boxes from 'Comtec' or somesuch (can't remember now) back in 2012, but available here on Bristol Communications and Electrical.
https://www.bcedirect.co.uk/products...side-joint-box
They also do the dropwire and PJ connectors. I had to do this because the builders doing up the house cut the original dropwire! Never had an issue with BT. Strictly speaking, there could be, but I've also had the Openreach lot around to do jobs and they willingly left me to finish them (just nipping up a few connections, etc...). I suppose this allowed them to make up time before moving to their computer-dictated next job.