Double quote key produces an umlaut-how to change settings?
 

I get errors when compiling because the double quote key produces an umlaut character. This happens in text editors (nano, gedit) and in .odt files.

I have checked keyboard settings but can't find anything useful.

Have you tried the Locale settings? Usually set up in init.d or /etc/profile by distros. Also perhaps other places.

Isn't this for language etc? My setting is UK English (followed by US English).

You seem to be using a US International keyboard driver. If you have a 104-key US keyboard (horizontal enter key, wide left shift), you need the ordinary US keyboard; otherwise, the GB or NL one depending on whatever you have.