6 hours ahead of time? The check-in counter opens 3 hours before the flight.
If you are able to check-in online and are not checking a bag I'd find something to do outside of the airport in the general area and once checked-in I'd spend the 30 pounds to access a lounge for some food & drink as LGW is essentially a giant mall.
Not sure if they have any issues with reprinting boarding passes at the check-in counter as those tend to be more of a low cost carrier rule.