When playing back streaming content from the App, TiVo allows you record 3 programmes simultaneously. However, when playing back iPlayer content from the Catch-Up EPG while recording 3 programmes, TiVo will ask you if its OK to stop recording on a tuner, in order to use it to play back the legacy VOD stream.
Virgin Media Staff employee BenMcr posted on Virgin's Help and Support Forums that:
The iPlayer app is staying on the Red Button, because it has more content than VoD does. However if you don't want to use it, you can find the iPlayer VoD content via: Catch Up On Demand, Backwards EPG (and) Search and Browse so there are more ways of finding the content than there was with the V boxes