The only way I have found to achieve this is as follows.
Watch live TV e.g. BBC 1 HD
Press OK
Press Down Arrow (below OK button)
Press Down Arrow again (On my screen I now have info about BBC 2 HD)
Press Right Arrow (That then shows a list of programs for BBC 2 HD)
Press OK (Brings up information about the current program on BBC 2 HD without changing to it)
I tried entering the channel number instead of using the Arrows but found that did change to the channel number entered.
Admin Edit:
Details added as an FAQ, many thanks.