During the London 2012 Olympic Games, the BBC provided 'Red Button' access to an extra twenty four HD channels (and their standard definition counterparts) via satellite dedicated to showing the most comprehensive coverage of the events as possible.
Viewers watching by terrestrial Freeview had the reintroduction of the second 'Red Button' stream on LCN 302 made available by the temporary removal of BBC Parliament, whilst spare HD capacity allowed the creation of '301 HD' on LCN 304.
The BBC's 'Red Button' service as seen on Sky.
On Freeview, the 'Red Button' service is necessarily a lot more limited.