I have added menu separators on this page http://79.170.40.241/refthecoffeefactory.co.uk/home
I have also added the following to remove the boarder on the far right of the menu, although it doesn't seem to work.....
#navigation ul.nav > li.menu-item-56 {
border-right: none !important;
}
Any ideas as to why?
Note: just took a further look. Your border is on the "a" tag, not the table. Still, my previous answer follows:
Looks like it's being overridden by other styles. Looking at your style chain, you have many overlapping styles and use !important a lot. There are ways to isolate that particular element, but you might want to revisit all your styles taking specificity and inheritance into account. Here's a site that explains it simply and effectively: http://www.vanseodesign.com/css/css-specificity-inheritance-cascaade/
Also, to find out which style is specifically breaking it, with Firefox or Chrome, right-click and inspect element. You'll see that the one where you specify no border is overridden (it's crossed out).