Hi,
I have a youview box. When I select iplayer through the on demand players menu I get the choice of HD content. If I select content through the guide do you have to be on channel 101/102 etc to get HD versions or should it do it through channel 1 2 etc etc. I've got view HD enabled in the menu of the box. I do hope that makes sense.

I tried top gear on channel 2 and through the guide and it was in SD. If I manually select iplayer again from the players menu it's there in HD

Not really sure what you mean, but in the iPlayer you should be able to toggle HD On and Off if it's available.

To view HD Freeview content on your TV, in the guide you need press the relevant HD channel EPG number. The box won't do it for you. Though it will record content in HD if it's available. Clever trick that.

When you watch a BBC programme, it offers you the choice of watching the HD or SD version.

You have to turn on the prompt for HD content in the menu system. It's under Settings>TV SIgnal & Quality>Play In High Definition