Simply login to your hosting account at www.shouthosting.co.uk/billing/whmcs/clientarea.php
Click on 'My Services' in the top navigation bar.
Your active service will now be highlighted in green.
Scroll accross to the small icon at the end of the green bar (showing a green arrow) And click on that icon.
You will now be taken to your 'Product Details' page.
Scroll down where you will find two buttons. You will see that one of them says 'Login to cPanel'
You can click on that button to login OR scroll a little further and you will see that your username and password is shown. Simply use those details to login as usual.
NOTE
If you changed your cPanel password from within cpanel itelf, the details shown in the area mentioned above may not work. In such cases please seek further help by contacting support where a new password will be emailed to you.