How to make an un-clickable custom link on menu

I want to make an un-clickable custom link item on my primary navigation menu. I want this item to be inactive, but allow me to add sub-items.

In another theme which I use I can set the URL to http://# but this doesn't work in GP. When I save the menu and then click on the 'un-clickable item' I open a new blank page.

Is there any other way I can achieve the same thing?

Many thanks
Chris