I've transited through LHR Terminal 4 several times in the last few months (as a CO Plat). Each time going on a CO flight to the US I've gotten access to Holideck. Going on a Kingfisher flight to India, though, access was denied with the ST Elite+ / CO Plat Card.

IME the food and drink offerings were better than PCs in the US, though there didn't seem to be free wireless like at PCs. More crowded furnishings and odd decor.