Just to close this off, after a couple of days of looking at offers on websites and then ringing around to get better information, I've selected a supplier, Plusnet, and booked the changeover to FTTC. I've been given a date of 14th November, which sounds reasonable, and now have all the kit set up and ready to go, with a PoE powered ADSL/VDSL modem (an unlocked Huawei HG612) right next to the already fitted NTE5 Mk3 connection.

Lessons I've learned from this process have been:

Getting the truth out of sales people is like pulling teeth. Some are better than others, but generally you get fed some pretty wild tales when they are trying to sell you a package.

Pinning down the cost of individual elements of the package is exceedingly hard, and some suppliers simply won't do it, they have an "all or nothing" approach. For someone that knows what they want in terms of a broadband service and phone service this can be extremely frustrating.

Some suppliers seem to be so confused as to what they can or cannot offer that they got binned as possibilities early on. Sorry EE, but you fall into that category.

Finally, I've read up about some of the issues people have had with many suppliers, and on balance chose Plusnet really because they were technically far more on the ball than any others when I spoke to them, their package offerings allowed us to pick and mix exactly what we needed and their prices were reasonable - not the cheapest, but not the dearest, either. For our needs they seemed to be the best choice, with TalkTalk coming a close second (in fact the only real reason not to go with TalkTalk was concern over their data security after they were hacked a while ago).

The help from here has been invaluable in improving my understanding as to how FTTC, and the systems behind it, work, and that in turn helped when I was talking to possible suppliers, so I'd like to thank everyone who contributed to this thread.

Jeremy