HiDef is LoDef

Black Hole

May contain traces of nut
I'm watching the rugby on BBC1HD and the sound quality suddenly changed and the picture has gone LoDef. Worse than StDef. BBC1 is the same.

Seems to be OK again now, I didn't notice the switch back because I was flicking around channels and native TV to see what's what.
Just started watching my recording now. I take it from your posting time this happened near the end of the match?