Ok, further research has led me to a temp fix, if you go into your General Settings within your profile & change the editor style from WYSIWYG to Standard, it then lets you use the enter key.
Also some admin of another site has said "I've set the server to tell IE to render all pages in IE9 mode, this should fix it until either IE10 or the editor is fixed."
I understand there's a number of addons & hacks to make things work in harmony with eachother, but it does seem IE isn't high on the list of friendly browsers for the site, but is the most widely used around the world, maybe not the forum, so would be great if we could get better compatibility.