You can access your M: Drive off campus using Secure File Transfer Protocol (SFTP). We recommend using the FileZilla Client but you can use a different client if you want to - just skip to the settings part.
Open FileZilla and choose File → Site Manager... → New Site
Give it a suitable name, for example 'M: Drive', and then enter the following settings:
Protocol SFTP - SSH File Transfer Protocol
Logon Type: Normal
User: your University username (do not add @essex.ac.uk after your username)
Password: your University password
Click OK if you're asked to confirm the host's key fingerprint.
Once you're connected you'll be able to see all of your files and folders stored in your M: Drive. To download or upload files simply drag and drop.