VBA - Close Internet Explorer popup window

I am currently using the following code to open an Internet Explorer window, so that I can fill out and submit an online form.

Dim IE As InternetExplorer
Set IE = New InternetExplorer

With IE
.Visible = True
.Navigate "URL"
End With

However, when I go to the page in question a pop-up window appears. I therefore need to be able to close the pop-up window, or make the original (parent) window active, before I can submit the form. Does anyone know how I can do this?

Any help much appreciated - Thanks