Looks as though there is something wrong with one of my files, as I have looked at another cart from a member on here and it is very stable.
I have looked into this further and it would appear it may have something to do with the introduction of the cart following the page. The other members site I tested which is stable on a mobile, does not have this feature on his website, the cart is static.
If I scroll down on my website the cart actually over runs into the footer which may be causing the problem.