How to redisplay a page in iPhone UIWebView

I've got a UIWebView which starts off with the scalesPagesToFit property set to YES. This loads up the page and scales it fine. When the user taps a button I want to turn off the scaling and show the page full size but I'm struggling to figure out how to force the page to redraw. I specifically do not want to refresh the page (ie fetch it from the server again) just redraw the page that has already been downloaded. I've tried setN开发者_Python百科eedsLayout and setNeedsDisplay but neither of these work