An update.....Router and antenna arrived at the end of last week, along with an unlimited SIM from Three. Tried it all around the house, inside and out, and I can't get a reliable 4G signal anywhere (we're are between 2 masts, both 6-7 miles away, behind hills). 3G seems to get a reliable connection with up to 13 Mb/s, which is about the same as we get from ADSL.
Openreach have been out and found 3 different places where the phone line is crimped over on a pole outside (which leccy guys had re-sited) and ADSL connection has been stable since then.
I'm sticking with the phone line for now, cancelling the Three SIM and putting the equipment in boxes until an unlimited Virgin/EE SIM comes out, whilst looking longingly at the EE mast 1000m away.....
Get an EE one then