Product attributes not filtering

[RobHannaford]

I have a magento store with multiple variations. If I have two selectable attributes and I select something on the first one it is not filtering the second selection to only include products with the 1st selection.

Any ideas?

Addition to this I can also select from either dropdown and I'm sure this is wrong and is why I am getting the problem.

See here: http://www.gsworkwear.com/portwest-hi-vis-rain-trousers-h441.html