When the same OnDemand programme is available from multiple sources, your V6 will, under "Watch now", list the different places.
Chargeable options are always listed first, that's the nature of the beast. Scroll down past the "Virgin Media Store" or whatever you've got, and "BBC iPlayer" should be an option - and that'll be free.
If you're finding the programme directly from the reverse EPG and clicking "Watch from Catchup", this should take you to the same screen.
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