Channel 4 have updated their TV on demand for iOS device. Version 3.3 of the app fixes download issues that been affecting iOS 7 users and includes other stability improvements. The iOS app is free but to use the downloading features you will to sign in to the app (with a free account).
What’s New in Version 3.3
Version 3.3 addresses bugs some iOS7 users experienced with Downloads.
It also includes various other stability improvements.