The Luton-based airline, founded by Greek millionaire Stelios Haji-Ioannou, bought its rival Go last week for £374 million. It has set itself large expansion targets, which it must meet to stop another rival, Ryanair, from reclaiming the number one spot in Europe. As Mr Hahn-Petersen wrote the letter on Wednesday, directors were celebrating a 62 per cent rise in passenger numbers last month. He said they recognised the strain employees were under and that more staff would be trained.