iPad putting random spaces in customer number
The iPad doesn't do that, it's determined by the author of that site and how they treat a mobile device.  The iPad can't tell what kind of data field that is.  I recommend you contact NS&amp;I and tell them about it.

Meanwhile, tap the Share button on the top-right and select `Request Desktop Site'.  The page should refresh and provide you the desktop version of the site instead of the mobile version.  See if that allows you to enter your customer number.  This site can help show you how to do that.