Dances with Boffins,
Just to put the record straight. Serco do not set up a separate company for each contract. Each contract is bid and won as a separate entity and works to their own budget. Bahrain and all the UAE contracts are part of Serco Middle East, which in turn is part of Serco Group.
The reason for losing any contract would normally be at the rebid and could be for a number of reasons, but as you say it would not affect any other contract.
RD