The hosts are Fasthosts and they continually change server settings without letting customers know first.
Their reply to this is...
“We are unable to stop the error from being generated, but it looks like the issue here is that the site itself is displaying the error as part of the content of the page.
This will either need to be disabled via a script or perhaps via a setting if your site is a drupal or wordpress site or something like that but you will need to do some research online into how to do so. Depending on the platform it may not be possible (as from the forum I found it looks like this is not yet a feature of drupal for example).“
Looks like i’m going to have to disable errors on every page. Urggh :(
...and what happens now if an error is genuine? I’ll have errors turned off and will be none the wiser.