These are the facts:
The GB Airbuses were NOT and never were intended for BA. They were ordered as part of the BA order so that both, note, both BA and GB Airways got a better rate on both the airframes and the engines this was beneficial to both, note again, both parties especially BA who take an extra cut.
GB Airways has existed since the 1930's it is a company with a long history.
Not all routes are ex-BA routes. Most are GB Airways own routes which they have built up through hard work and determination.
I.e. Gibraltar, Valencia, Alicante, Seville, Agadir, Marrakech, Malta, Nantes,Teneriffe, Las Palmas, Lanzarotte, and they have recently announced Almeria. Casablanca and Tunis were originally BCal (- dropped by BA)
Those routes which BA gave to GB they claimed they could not make pay. Montpellier for example was dropped by BA, (this was originally a Dan-Air route). It was NOT transferred to GB. GB saw an opportunity and grabbed it. Note Ryanair is now on this route, I suppose the Ryanair pilots are stealing the birthright of BA.
GB do not get subsidised handling. They pay slightly morethan market rate for BA handling ,for supposedly a premium product. To those in BA unfamilliar with the concept of market rate, this is what the rest of the world, including your competitors are prepared to pay. They do not pay for white-elephants like WaterWorld and its not-working part-time employees all on above market rate salaries. This is why BAs internal charges are so high.
Go, Ryanair, Easyjet etc. are the competition. They do not pay above market rate for anything why should GB Airways if it wishes to compete.
The employees and management of BA need to get out in the real world. Most believe they are still in BEA. GB has had its share of BA reject management who inevitably try to turn it into BA. This is why there have been 6 Managing Directors within the last 13 years (one, not a BA reject actually lasted 5 years).
The owners of GB Airways are no fools. They know they have one of the best most profitable airlines in the UK. I suspect they know BA are in very very deep trouble. As far as they are concerned it may only be a question of waiting...........