Can anyone identify the problem with my Grapevines?

That looks like blistering and damage done by environmental factors to me, rather than anything nasty.  It looks like your vines are inside a polytunnel.  It may be scorch from too much heat or sun.

The vines will be dropping their leaves soon anyway, so I would just leave them alone for now 

It could indeed be one of the mildews, the commonest diseases of vines. Downy mildew can be easily told from other damage as New Shoot describes by putting a couple of affected leaves in a plastic bag moist, like covered with moistened kitchen towel or such. Within a short time white fungus like substance shall develop, if it's mildew.

Like a day or two.

To me it looks like these leaves have have come to the end of their life, I have the same thing every year. When where the pictures taken?

Pics were just taken 3-4 days ago. The problem leaves have been on the lower leaves of my largest vine for about 2 months but didn't start to show up on the other smaller vines until much later. I have 2 black hamburgh, 2 Boskoop glory and 1 fosters seedling.