I have a Macbook Air (13-inch, Mid 2013) running OS X El Capitan. Prior to upgrading to 10.11.4 pressing SHIFT + 3 returned the £ (pound) sign and alt + 3 returned the # (hash) key. Since upgrading these have been reversed! Can anyone advise how to switch this back? Why has this happened?
It seems that after upgrading my keyboard settings have been changed from US to UK. To fix the key binding issue described above I needed to go to:
System preferences -> Keyboard -> Input sources and click the + button to add UK as my input source, then delete the US input source in the menu of the LHS. Thanks very much for Mark for getting me to check this.