It's not from the BBC, it's from the EBU. Presumably the BBC only have a copy with their own commentary on it.
Collecting the archive took us some years. With the help from many broadcasters, we can combine image and sound so a clean version becomes available. For 1974, a part of the voting is only available with Dutch commentary. So don’t be surprised a bit later on! #eurovisionagain
— Stijn Smulders (@stijnsmulders) May 17, 2020