Given the recent growth in HDTV broadcasting, it was perhaps inevitable that the BBC would plan to have more than one high definition TV channel in order to avoid an ever-increasing risk of programme clashes caused by overrunning live events, hence the launch of a full BBC One HD simulcast channel this autumn.

However given the BBC's laudable "all or nothing" approach where national services have to be duplicated across all three major broadcast platforms (cable, satellite, terrestrial), a second BBC HD channel on terrestrial Freeview was until recently a very awkward prospect because there are currently only four or five slots available for HD channels.

Originally it was intended that the BBC should only be given one dedicated Freeview HD channel in the single, widely-available public service HD multiplex, with other public service broadcasters (Channel 3, Channel 4, Five, plus S4/C in Wales) being given one HD channel each.

This remained the case until Channel Five was forced to abandon its allocated terrestrial HD channel slot due to financial reasons, giving the BBC an opportunity to automatically claim Five's slot under rules drafted by Ofcom, which it has now done with the forthcoming launch of BBC One HD this autumn.

If Channel Five had been able to claim its Freeview HD slot, the BBC would have had to continue in the short term with a piecemeal HD service using either only one channel or borrowing additional space from another broadcaster such as S4/C or the aforementioned Five (who had planned to sub-let some of its HD slot anyway).

There's also the slim possibility that Channel Five under new ownership might subsequently try to claim its former terrestrial HD slot back for its own use - which it could still be entitled to do before 2012 - but the consequences of such an action wouldn't be popular with the viewing public (for one thing).

It's also interesting that the BBC HD channel will continue to exist alongside BBC One HD for the time being as opposed to having two simulcast channels (BBC One HD and BBC Two HD) as widely speculated prior to today's announcement, or two dedicated BBC HD channels (awkward for political reasons since that would represent a new service).

BBC Two HD is still likely to become a reality in the not too distant future (maybe in time for the 2012 Olympics), but the very fact that the BBC now has two HD channels could throw an uncomfortable spotlight onto the remits of BBC Three and BBC Four in particular, regardless of their individual merits.

Because BBC One HD and BBC HD together could end up posing an awkward question for the corporation: why continue with broadcasting four 'mainstream' channels when two could theoretically be just as capable?