var filePath = 'http://www.southeasternrailway.co.uk/widgets/embedded/live-travel-info/widget.php';
var iframe='<iframe id="widget" name="widget" src ="#" width="100%" height="1" marginheight="0" marginwidth="0" frameborder="no" scrolling="no"></iframe>';
document.write(iframe);

var aspectRatio = 2.1;

var myIframe = parent.document.getElementById("widget");
if (myIframe.clientWidth) { 
	myIframe_width = myIframe.clientWidth;
} else {
	myIframe_width = 200;
}

var iframeWidth = myIframe_width -2;
myIframe.height = iframeWidth * aspectRatio;
myIframe.width = iframeWidth;

myIframe.src = filePath;
myIframe.style.border = "none";