I need a regex (to work in PHP) to replace American English words in HTML with British English words. So color would be replaced by colour, meters by metres and so on [I kno
You don't need to use a regex explicitly. You can try the str_replace function, or if you need it to be case insensitive use the str_ireplace function.
Example:
$str = "Color: red
";
$new_str = str_ireplace ('%color%', 'colour', $str);
You can pass an array with all the words that you want to search for, instead of the string.