Yeah, i recall hearing about slots at heathrow when BA tried to buy Aer Lingus lately (the irish national airline is at least part-owned by the state, and though profitable, there is a big rush to sell off state assets for short-term gain, and austerity, and such...)
Anyway this became an issue because Ireland is an island, and getting off means going by air to Heathrow and then on to your destination ( cause you can get a flight to pretty much anywhere from London - of course you could take a ferry, but it is about 8 to 11 hours from Dublin to London by ferry/train, depending in connections...)
Anyway, the big issue is, what if this new BA super company doesn't bother to keep that extra slot at Heathrow where all the Irish like to land? Is tue national interest really served if we are isolated from the rest of the world? I did have some reason to wonder, how can a single slot be worth billions...