I know you're probably in LHR now, but did you mean the check-in queue or the security/immigration queue? As one of the most effective airports, I've never seen a 50min queue at either even on the peak travel times in Korea. But anything is possible. If it is the security/immigration queue that you are mentioning, remember there is more than one area. Some people think they must go to the security area closest to check-in which if a few flights have opened check-in at the same time can get crazy. Walking a minute or two to the next one could save you tons of time at security and immigration and have you in the lounge in no time.