Thanks for your reply @jbrennard
I do have an TP-Link Archer C9 which I have used in the past (when I was last on VM) to support our wifi signal, it's getting long in the tooth though and I worry about lack of firmware updates for security. (The hub 3 also gives me warnings for TKIP on it's out of the box settings, incidentally, but I know how to turn that off).
I was hoping signing up to a new contract I'd get some more modern equipment and I wouldn't have to shell out for my own - though it has been my experience in the past that ISP routers are hit and miss. It would be nice if they didn't keep pretending they worked really well though. There do seem to be some rare exceptions like Zen, who I would consider if they still did G-fast or we were in an OpenReach FTTP area.
In regard to Sky, they have a "wall to wall" wifi guarantee where they give you money back, but it's a lousy 3Mb it has to be below, so I'm not sure it's much to boast about either.
That being said, the Sky hub has been very reliable, their customer service really good, and they are one of the few to offer 150Mb via G-fast to us. I was going to stick with them, but I loathe the practice of mid contract price hikes, so I took the opportunity to show my displeasure and upgrade slightly to 250Mb with Virgin. I do appreciate all ISPs have been doing it, including Virgin, but unless it costs them in the pocket they are likely to keep at it. Hopefully the regulator will crack down on them and they'll stop with the one sided contract clauses in the future. From my point of view, if they want to increase your prices then you should be free to leave at any time.
Someone from Virgin has contacted me in a PM. The light is definitely red and not magenta - I don't know if it's actually showing anything wrong though. Apart from the poor signal in the kitchen, things seem as expected. My office is in the garden - I don't expect a fast signal out there, but it would be nice if it worked reliably with my smart devices at least, and I didn't had to give them an extra monthly fee for a simple wifi extender.
I've noticed that Virgin also don't let you change your IP subnet anymore either, so I will have to reconfigure things for that too. But at this point I've just turned the hub off and switched back to Sky so I can do a comparison. I've been putting off buying an overpriced mesh wifi solution, but looks like it might be the only way to work with the options I've got.