Airline says numbers must be reduced at bases such as Stansted and Manchester

Ryanair has written to UK pilots asking them to take unpaid leave or transfer to other bases abroad, saying they could otherwise join the 9,000 job losses at Thomas Cook.

The airline, which reported profits of €1bn (£886m) in May, told its pilots that a “significant surplus of pilots must be reduced” at UK bases including Stansted and Manchester, and that it was encouraging them to take up to 12 months of unpaid leave.

It said that there were limited vacancies for full-time pilots at bases in Morocco, Romania and Hungary.

The memo, sent on Tuesday, said: “With yesterday’s collapse of Thomas Cook with the loss of 9,000 jobs in the UK and potentially a further 13,000 jobs across Europe, we hope that there will be sufficient applications for unpaid leave/part time, so we do not have to resort to job losses at [your base] this winter.”

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It blamed the delay to Boeing 737 Max deliveries for the decision. Ryanair had ordered up to 135 of the aircraft for its expansion plans, with the first planes due this year. The model remains grounded, however, since the Ethiopian Airlines and Lion Air crashes.

The memo came a week after UK pilots called off the remainder of a series of strikes this month. The pilots union, Balpa, had complained about Ryanair’s “abysmal approach to industrial relations” and said the dispute over pay and conditions was driven by resentment over a range of cost-saving measures used by Ryanair.

Ryanair had called the strikes pointless and managed to operate the majority of its UK schedules by bringing in more contractors and pilots from overseas bases. The airline had warned of winter base closures across Europe.

Last week, the chief executive, Michael O’Leary, was awarded a new pay package in which he could receive a €99m (£88m) bonus within five years, although almost half of Ryanair shareholders voted against it.