At times there are files on the server with a users ownership. Ask your host to give a check on the server using the find command.
I believe that your web hosting provider will help you the best in such situations. I would always use a help of web host to start invistigate such situations.
I believe web hosting company will never refuse to help you.
Many thanks for the extra ideas. Have approached the hosts about it.
The 2 images attached, represent one of the domains.
/tmp has a lot in it that could possibly be cleared up, but I would guess your control panel is including itself and all the OS files in the total count.
With regards to the bots, thats normal and expected - plus, its perfectly easy for me to fake a hit to those, either by going to robots.txt myself, or via User Agent switching (making my browser look like something else).
Thanks, so what do I do first?
Open your file browser / ftp and browse to /tmp, look at whts in there and see if theres anything you can delete 
I couldn’t find it in the browser or the ftp - to do that in the browser, would you need to input www.domainname.com/tmp ?
Try using a FTP client to access the folder. In the root of your account you will see the tmp folder that will include stats.
Thanks James, they’re not there? Is there something in filezilla or somewhere else that I have to enable?
No, it should just show if you have access to it via FTP.
If its not showing, it may well be that you can’t edit files via there - however, as there was only ~150MB its not a huge amount of space.