It could be any. It's just a quirk of DVB-T that you can see the interactive channels. They aren't meant to be seen, but accessed only through the red button. Only 105 remains "constant" as BBCi, although even that could change if some dire emergency forced it.
It is a frequently quoted myth on forums that they are separate broadcasting channels. They are not!
There is a schedule published somewhere of what will be on the interactive channels, but AFAIK, it still doesn't allocate a particular channel to them.
What is carried on what can change at any time. As the referencing is done through the red button menu any change is transparent to the viewer.