28px margin being added to the html

I’m having an issue with a 28px margin being added to my wordpress install when I add a custom menu to a widget. Its definately this thats causing it as when i remove the widget it removes the margin

I’ve done a lot of searching and there’s many threads about the admin bar etc but its nothing to do with the admin bar, as the admin bar is showing and then underneath I have the 28px margin.

I have a header and footer included.

Can anyone shed any light on why this is happening?

Cheers