I'm from the UK going on a long trip on which I'll be using local SIM cards for my phone. While I won't be using my UK mobile number during this trip, I want it still to be there when I get back, to avoid the inconvenience of memorising a new number, getting all family friends and contacts to store the new number, etc etc.
I've heard that UK mobile phone providers will permanently, irreversibly cancel a UK mobile number if it is not used for "a few" months, and that their policies all vary widely - e.g. some require an actual connected phone call while others allow missed calls or text messages, with some it's three months, others it's vague and undefined, etc.
No phone shop staff seem to know what these policies are other than that they exist, and nor do call centre staff. If they are published on mobile network provider websites, I can't find them.
What can people do when travelling for long periods like this to stop their numbers being turned off?