Scroll not smooth as on other page.

[theremotedr]

I am using a scroll on my pages but on one page it is jerky in its operation compared to the same but on the other pages.

I looking on the iPhone and below example is spot on.
http://www.theremotedoctor.co.uk/karford.html?scrollto=selection

But here is the jerky page in question.
http://www.theremotedoctor.co.uk/victorias_attic.html

It's the back to top scroll that is affected.
Checking the code like for like I don't see any mistakes etc so don't understand why it's not smooth etc on the page mentioned.

Please take a look and advise.

Thanks.