I'd give Zen a swerve. I don't have their FTTP, but I have their FTTC. The connection itself is rock solid and I have no complaints on that front, but the customer service and general user experience has gone downhill a lot since COVID.
You can call up, and (eventually) get someone in the UK, but if you have an issue that requires more than one call it's pretty much impossible. The person who dealt with you last time is invariably unavailable, and they don't seem to take any notes, and you have to explain everything again from scratch, over and over.
Additionally, they now seem to have two user portals/control panels for apparently no reason. The old one (in my bookmarks) works, but the new one (which they now point to from their website) doesn't recognise me as a customer and doesn't let me log in. It shows up a poor level of quality control to me.
I'm paying above average for a 40/10 service on the basis that it's Zen, it's a good old-school British ISP and it's got better-than-average customer service. I've only not switched because I'm moving, but I'm not considering Zen at the new place. Openreach DSL is Openreach DSL, and Zen is nothing to write home about, I may as well be with Sky or TalkTalk and pay less. I'd look at AAISP as mentioned above - they will know what they are talking about and be able to help to a much higher level than Zen.