BBC2 was always Helvetica as far as I can tell. I don't recall seeing any examples where the font looked a bit different, except once where the programme name was keyed on instead of part of the slide. This only applies to the standard slides with the BBC2 logo and programme title in white in the bottom left corner though.
WIthout knowing what five have planned for next year, I am wondering whether the current "fad" of custom fonts is now coming to an end? BBC2 opted for a proprietry font in February and I see that E4 - probably the pioneer of custom fonts - appears to have ditched BOTH its Fontsmith typefaces for the one used on the ITV Schools clock in the 1960s!
Similarly, an ITV3 Christmas trail I have just seen used Gill Sans for the word "Christmas". The fickle world of television branding eh?