[Spencer]

BBC also has a 100% subtitle requirement for all its channels (BBC Parliament excepted, though a good chunk of it actually is subtitled).  So the subtitles tag is pretty much redundant as far as the BBC is concerned. 

Pretty sure CBeebies doesn't plonk a subtitles tag at the start of its programming either, though can't be sure if this is promoted in other ways.

Exactly, it doesn’t need to be there any more if subtitles are already the default, in my view.

It’s just clutter on screen.

It’s a view clearly shared by various other broadcasters including Channel 4. But the BBC and ITV seem to want to keep in line with Ofcom best practice.