How can I make some pages wider than others?

I’m currently trying to configure a webpage which contains an iFrame window. This window is bigger than the page it appears on, however, so you need to scroll within the window to see it all. Is there some piece of code I can add to this particular page to make it wider?

The page I’m talking about can be found here: http://rivercottageteesdale.com/availability/

Thanks, J