The offices behind checkin are more likely to be load control and close-outs. I'm pretty sure that they aren't crew rooms, as VS crew tend to check in within Queens Building. This building is also used by BMI and a few other airlines with large operations at Heathrow.
British Airways is an exception - they have their own report centre on the southern perimiter of the airport called Compass Centre.
What do we do there? We, um, get briefed for our flights, maybe have some lunch, watch some TV, you know - stuff.....