HI Guys
Ok ive managed to do this. there was a couple of issues that needed to be addressed so Id thought id share my experiences with you.
One of the things ive found is that I couldnt find any fix variable for site_url, so within the context I had to create a key called site_url then the value of the key would be
https://www.domain.co.uk save changes and clear cache from the modx manager, but also remove all files/folders in the core/cache folder on the server.
another problem i came across is that the url's to external fonts, rather than using the achual path
http://fonts.google.com........ you need to ensure that the url starts with //fonts......
I didnt use the .htaccess file to 301 redirect / pages from http to https, instead I changed the available-sites configuration file within the apache config to handle all the forwarding. this is a better way in doing so, over the .htaccess file.
