I've only taken BA HEL-LHR (and AY LHR-HEL ... a flawed strategy) and traveling on BA does not allow using the longhaul lounge. Maybe AY is different. I think there was a security checkpoint between the BA gate and the longhaul lounge so it wasn't even possible to get to the longhaul lounge (without a longhaul BP). But it was early in the morning, and HEL makes for late nights, so I may not have been the most observant. I do remember being surprised at how bad the coffee was in the lounge, somehow I expected better.