Actually they don't, these slots can be used for whatever anybody wants. If they end up being used on a route that BA is currently on then great, more competition.
That's not true. There are grandfathering rights after the slots have been used for a certain number of seasons but the usage of the slots is perfectly clear:
IAG - International Airlines Group - News Release
IAG has offered the following commitments to the EC as part of the regulatory process:
· Seven daily slot pairs to be used between Heathrow and either Edinburgh and/or Aberdeen.
· Five daily slot pairs to be used between Heathrow and the following destinations - Nice, Cairo, Riyadh, Moscow, Edinburgh and/or Aberdeen.
· Two Heathrow daily slot pairs will be leased to Transaero for use on flights to Moscow.