I can't see the Gov being that concerned about IAG taking over BD as the only other potential BA have to expand from London is the remote and contentious possibility of the Thames Estuary airport, which BA don't want. How can they grow their business in the UK without more capacity at LHR? The collusion that there has been on air fares over the years would seem to suggest that it doesn't matter whether there is a competitor or not, the consumer will get stuffed anyway.