In reply to Kimono:
> The apps were doing an IP address check before launching to check I was in the UK, but if I then knocked the VPN off
> could you explain this please?
When you try to start an iPlayer program it uses your IP address to try and work out if you are in the UK. If it thinks you are not then it gives you the message about only being available in the UK.
If you have your VPN on, you have an IP address that makes you appear to be in the UK and the program will start.
Many systems often do no further check of your IP address - so if you switch off you VPN after the program has started it will continue to let you watch it.
The benefit being, if your VPN is adding a bit of latency or effectively throttling your bandwidth and your programme is buffering a lot, then by switching off the VPN you go direct to the BBC and get the best speed possible.
Always seems to have worked for 4OD in my experience, shame there's not much worth watching on it.
In the past with the BBC iPlayer, sometimes this has worked and sometimes not - depending upon which sort of programmer has been let loose on the latest version of the player.
I've just tested it now and it is currently letting you do the switch mid stream.