Re: "with rival network operators complaining that Openreach is unfairly undercutting them"
They've always done that kind of thing.
I've had the same problem with leased lines.
One workplace, they ordered a leased line and the only place that served us anywhere near reasonably was BT.
I took over the IT three years later. No leased line. Every six months or so, someone would kick up a stink, force BT to do something, they'd come to site, put a piece of tubing through somewhere, and then leave site never to return. It happened so often, the tubing they used changed several times over the course of those installs and was always left in place (eventually, there would have been a point where trying to join that tubing simply wouldn't ever have been possible without replacing the tubing from previous installs).
I decided not to propagate this nonsense when I took over. All the availability checkers said that there was no existing connectivity to the (quite rural) site, except through BT. So unless we wanted to spend six-figures-plus on installing a line to the nearest town, we could only use BT. That's what the availability checkers repeatedly said for all kinds of companies we tried.
So I decided to ignore them. I went straight to Virgin Media and told them our problem. They realised that actually they had a customer nearby which they could piggy-back off, and because of the rural postcode thing it wouldn't have appeared on the availability checkers. We put in an order with them.
Literally THE NEXT DAY, I had BT engineers crawling over our (privileged) site, uninvited. I had them removed. They were suddenly trying to put all the tubing and blow the fibre in order to complete a THREE YEAR OLD installation contract that they had never fulfilled. We escalated that with them and cancelled the contract. They tried to resist, and kept turning up to site uninvited to "complete your install" even after the contract was cancelled. BT claimed all kinds of contractual disputes with us, and then I said... okay... install.
Turns out - and I already knew - that they couldn't. The local exchange simply never had capacity enough, and never had enough, to install our line anyway. I know that, because their engineers knew that, and a cup of tea and a chocolate hobnob go a long way.
When they finally admitted that, we told them never to contact us again. We even terminated our ISDN/analog lines and went full SIP once the VM leased line was up.
And the VM line went live just a few weeks after our order with them. It's still in use, still doesn't appear on the availability checkers, and has provided flawless service for nearly 10 years now, including a 10Gbit upgrade.
So for three years plus, BT were basically pretending to install our line, never had any intention of doing so, and couldn't even if they'd wanted to without huge investment in the local exchange (which was never going to happen). Then they lied about it, tried to bluff us repeatedly and somehow found out that Virgin were delivering a line and then IMMEDIATELY turned up to try to look like they were doing something about it once again. And action only happened ONCE we basically found a way to use a competitor that they thought they didn't have.
As far as I remember, there are still about half-a-dozen unoccupied pieces of tubing underneath various buildings at that site, that never were joined, touched or filled after their install. And a shiny VM line right next to them.
Another part of the same site, about half-a-mile down the road... sadly BT only. Virgin say they could deliver to it but the costs were stupendous because it's the wrong direction (i.e. further away from their kit). We got another leased line over there (for connecting sites and for redundancy) from BT and we have nothing but trouble with it. They delivered only TWENTY MINUTES before our final, business-critical deadline that we informed them of nearly a year in advance, leading me to have a full and complete backup plan in action involving point-to-point wifi and church steeples (and I already had all the permissions lined up, I just needed to say the word). The engineer who finally saved their butt on delivery of that contract nearly got himself removed from site too, because he was so rude (mainly because his bosses were telling him that this HAD TO COMPLETE there and then and the guy took his frustrations out on his customer too).