Custom search not getting GET parameters from URL on live version

I have a strange issue where my custom search form works fine on localhost but not on live.

It uses $_GET to get the parameters from the URL and it looks as though these vars cannot be accessed on the live server but can on localhost. So if I do print_r($_GET) on the page with the search form the parameters from the URL are listed in an array on localhost but on the live site it displays an empty array.

Has anyone come across this before?