Cofnchtr:I believe some need an active SKY subscription as they are encrypted on the SKY platform but this may only be correct for the SD equivalents. (I await to be corrected).
BBC HD, BBC1 HD, ITV1 HD (London and Granada) and LuxeTV HD (or whatever it's calling itself now) are all FTA (Free To Air) so don't require a viewing card.
ITV1 HD (Central west and Meridian South) C4 HD, Five HD are FTV (Free To View) which as the name implies, are free, but they're encrypted, so require an active viewing card to receive them - That card can be either a Freesat from Sky card or even an ex-subscription card (provided its a current white card) no subscription is required for FTV channels
The above only works when you have a SKY+HD box or a new SKY+ box (essentially an HD box) as the older SKY+ boxes just give you an upgrade message.
Cheers,
Cofnchtr.
It works on any box, provided its a current white viewing card thats being used, you only get the upgrade message if it's an old blue with yellow house card which are all now deactivated....