Once again t-p thank you so much for your help.
I have had a reply from the host telling me they have fixed it, the reply read:-
“We did checked and confirmed there was a custom php.ini present under the WordPress installed directory, such that we have now disabled the same and enabled the required php.ini file for the mentioned domains.”
I’m concerned to know how that custom php.ini got there in the first place, could it happen again? I’m sure these are questions I should be asking the host!