Because of this:
<string xmlns="http://www.esriuk.com/gazops">
all your elements are in a namespace, and your path expressions need to use a prefix that's bound to this namespace. Declare
xmlns:p="http://www.esriuk.com/gazops"
in the xsl:stylesheet element, and replace expressions such as
test="//OPERATION_RESULT='No Match Found'"
with
test="//p:OPERATION_RESULT='No Match Found'"
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference