Use search:
RTMPDump and ITV Player?
www.itv.com: How to download free TV Shows from ITV Player
www.itv.com: How to download Silverlight video streaming

You can download videos from ITV. Note that a downloader creates a separate thread, so make sure your Internet connection is fast enough to allow playing and downloading simultaneously.

If you want to record ITV Player while playing, you can use screen video capture software like Replay Video Capture. Such programs can record almost anything from your screen. But you should have a stable connection with the server (without any buffering problems,...).