Hi
Thank you all, I'm going to call A&A tomorrow. Also interested in their VOIP solution as I'd rather have phone/internet with one provider, additionally BT is rather expensive if using them just for phone.
As an aside, today I re-wired everything (for the umpteenth time) adding a Tacima 6 Way Mains Conditioner and also my fourth modem (a Zyxel VMG1312-B10A).
As expected, no difference (3 drops today without warning) but the Zyxel does get a slightly higher rate sync, so I thing will work brilliantly on a non-fault line.
I think you have just approached it all from the wrong side. If you are having issues with the dial tone and making calls it means there is a physical fault on your line which isn't uncommon. You simply report the issue as a problem with making voice calls, they send out Openreach that will like just remake a few joints along the route and do some tests and likely resolve it very quickly. Once that is fixed, so is your broadband.
I've had similar issues a few years ago with broadband, going up and down and syncing slow with errors through the roof, noticed crackles on the phone line, reported it as voice fault, that got fixed, and internet was all okay again. If I had reported it to my ISP as a broadband fault, I'd still be on my knees plugging things in and out of the test socket whilst I reboot the router for the millionth time.
Regards
Phil