The contract itself may not make a loss but when you factor in the NSL overheads and wages of all the people who work for the company at CTC and NERC etc it is a different matter.
It is this very fact that has lead NATS to negotiate loss making contracts as without them a portion of these costs would not be met and NSL would be in even deeper financial straights. They would also have the architecture and infrastructure among other costs to write off if they let the contract go.
It is not as easy or simple as it first appears.
Hope I got most of that right, from the lions mouth today.