iPhone and Sentinel
If you have an iPhone 3GS, 4, 4S, or 5 running iOS 5 or later, you can use the Sentinel App - this offers the highest level of authentication.
If you are a Network Rail employee, you can install this App on your iPhone through the usual Network Rail channels. If you do not work for Network Rail and wish to download the app, you need to go to the App Store.
What about my iPad?
You can still install the Sentinel app. Please note that the Sentinel app is an iPhone app and therefore the size on screen is not optimised for the iPad - so it will only take up part of the screen.