I've spoken to Plusnet support after raising a ticket on our line. We had two separate issues, 1st wifi dropping out and 2nd a line fault. The line fault has been resolved and the support person directed me to this forum stating it will be escalated to the product team.
Since the New Year, Wifi has been sporadically dropping out for some lap-tops and phones. We also have an Amazon firestick which has had no problems. Our router is about 4 years old and has had no previous problems.
Wifi drop outs do not seem to be related to load as we can have 3 simultaneous Teams/Zooms calls (home-schooling & working) fine, but one person on the internet will drop out. I've followed instructions for not separating connecting to 2.4 and 5 Ghz, but no device (laptops, phones & firestick) is able to connect to 5 GHz (I understand some older devices won't connect).
When wifi does drop out, internet connectivity is not being lost as 1) not all devices lose connection and affected laptops can get back online with an ethernet cable.