Is there any quick way of deleting messages stored in the deleted folder

left click on the first message to highlight it > hold shift and then the down arrow (or page-down) until you reach the bottom > when they are all highlighted press delete.

Make sure that you definitely want to delete ALL selected messages cos when you press delete...they are gone!!

Or alternatively click on your Deleted Items folder, click on an email and press CTRL A.
This should highlight all your emails, now you can press delete