What a very helpful response
Thank you all. Getting two distinct approaches in the first two replies led me to the two obvious contenders - and I then spent quite a lot of time reading about them. I particularly valued the fact that one was EE based and the other O2 based as these are the two networks we already use.
Colin, G8TMV - thank you for suggesting GifGaf - I will PM you on this kind offer of a way of by-passing the O2 “theft” of my top-ups. (EDIT here as I got the network links mixed up.) (I think they have had more than £40 off me in the past 18 months with very little in return.)
Ray, GM7NZI and Simon, G7WKX - thank you both for pointing me at 1pMobile. I would have dismissed it as some sort of scam but with two (now three) recommendations it has to be a good alternative to EE, especially for the phone that stays in the car and is almost never used.
Ed, DD5LP - thanks for the warning on Europe. If we do go there it will not be for SOTA, or not much as M6BWA gets excluded, and I will research when necessary.
Nick, G8VNW - I am still considering the Vodaphone £1 charge for retaining the service for 6 months - 15p per month is very reasonable compared with the others, but I think I have missed a trick with EE and
thank Andy, MM0FMF, for the idea of the STOP PACK message.
Also thanks to Phil, G4OBK - for confirming the value of 1pMobile.
I think the first one to go is the old iPhone which has an EE SIM and gives me the message “SIM not provisioned”. What a nice old-fashioned euphemism for “Pay us yet another £10 for doing nothing.”
I will report here if anything interesting turns up as I check the existing credit balances and change SIMs as necessary.