- preg_replace: documentation ( source)
<?php
echo preg_replace('/%([0-9a-f]{2})/ie', 'chr(hexdec($1))', (string) "Industrial%2520%2526%2520Financial%2520Systems%252C%2520IFS%2520UK%2520Ltd");
echo raw_urldecode("Industrial%2520%2526%2520Financial%2520Systems%252C%2520IFS%2520UK%2520Ltd");