It gets better - some person has now told me this:
Stuart, even if you are using the home Wifi to access internet on your
mobile phone, you'll be charged. This is because the, if you connect to
the internet on your mobile phone using the home Wifi the data access
happens on the SIM card. This is reason you are charged.
Rubbish??? I have asked her to check her understanding of wifi charges as I'm certain that I should not get charged for using wifi. If so what's the point?