Okay - just in case anyone in the future reads this and wonders if I got it sorted - I did - as I think had been mentioned but with a slight difference. Total reset of the base unit as well as the handset. I'd only done the latter. So, you unplug EVERYTHING completely (inc the phone battery) - leave all for an hour++ then reconnect in a particular sequence - battery into phone first, then reconnect base unit THEN wait for 2 mins - then reconnect phone and keep the handset away from all other electrical equipment until you've done that. Wait another few mins and then test. AND IT WORKS!!!
Thanks everyone for pointing me in the right direction and think I'll stick with this for a shade longer now its functional again.