Thanks again Martin and while the signal downstairs is -112dBm, there is a fair -99dBm signal high up at one window upstairs. Would your recommendation be to but a signal booster then, with the antenna in the attic above that window?
Paul, that's really helpful and thank you. Yes, the signal boosters are an expensive option - especially if EE are doing some maintenance and the signal recovers!
The signal strength I used was 4G and you made me think that with one of the free apps the phone can be switched to prefer 2G. I have done that and while inconvenient to have to switch back to 4G when I go out it is an adequate and cost free solution with signal strength increased to a tolerable -99dBm. So will do that for the time being and see if in due course it all recovers. To think that only a couple of months ago the speed on 4G was better than on my BT fibre-to-copper broadband ...
Just remember that EE's 4G1800 footprint, by design, will never exceed that of their 2G1800 footprint. For the very obvious reason of CSFB. Or to put it another way, you should never have 4G1800 without 2G1800 also being available.
Thanks very much Paul and Japitts. The Tasker+switcher solution is a very good idea and many years since I last had to install it - with the switch automated to move to 2G when connected to wifi the solution will be good enough to be permanent ... while also hoping for the local mast to recover!