Thomas Cook shares have slumped after the holidays giant announced the shock departure of the woman credited with securing its survival.

Harriet Green, who joined the company in July 2012 when it had just tapped its banks for £200 million in order to stay afloat, said her work at Thomas Cook was complete after returning it to a sound financial footing.

Her campaign of cost savings and a purge of low-margin operations ensured underlying earnings rose by 44% to £323 million in annual results today.

Its stock market value has surged from £148 million when Ms Green joined to £2.7 billion earlier this year but slid by 20% or £400 million today after the surprise announcement.

As well as uncertainty caused by Ms Green's departure, investors were spooked by the company's warning that tougher trading conditions in countries such as France meant the pace of its recovery would moderate.

Ms Green's departure comes days after she told Management Today's Inspiring Women conference that the turnaround was "absolutely not done".

She said: 'You can't do a transformation on this sort of scale in a year or two years. I usually say it's about six years."

Ms Green has been replaced with immediate effect by chief operating officer Peter Fankhauser, who has been with Thomas Cook for 13 years and is credited with leading the turnaround of its UK division.

Under Ms Green's leadership the company cut costs through the closure of shops, as well as through the sale of hotels and reduction in its airline fleet.

Thomas Cook chairman Frank Meysman said: "Harriet has had a highly positive impact on this company.

"We emerge from her transformation stronger, with a clear strategy, world-class leadership team, updated brand, and a renewed focus on the customer."

Ms Green joined the company from Leeds-based technology distributor Premier Farnell, where she was chief executive. She received pay and bonuses from Thomas Cook worth £2.8 million in the 2012/13 financial year.

She said today: "I always said that I would move on to another company with fresh challenges once my work was complete. That time is now.

"I wish all of the team at this re-energised company continued success, as they move to the next phase of the company's development."

Cost and profit improvements under Ms Green's turnaround plan now amount to £400 million and should rise to more than £500 million by the end of this financial year.

The company added: "We have de-risked our business by reducing low profit and high risk operations, through business disposals, strategic reductions in risk capacity in France and Russia, and the removal from sale of low quality product."

The strategy reduced full-year revenues by £727 million to £8.6 billion, with the stronger pound and lower demand for Egypt holidays among other factors.

It offset some of the shortfall by generating £186 million in revenues from newly launched products, such as the roll-out of more exclusive holidays.

Including restructuring costs, Thomas Cook recorded a smaller full-year loss of £114 million against a deficit of £163 million a year earlier.

The company said UK bookings for this winter have increased significantly with volumes 5% higher than a year ago and average selling prices up 1%. Bookings in France are 15% lower with prices 3% higher.

It said: "Reflecting the tougher trading environment our outlook for growth in 2015, while still positive, is more measured. Accordingly, we now expect to deliver further growth this year at a more moderate pace."

Leisure analyst Mark Brumby of Langton Capital said the achievement of the group's full potential may take a little longer than shareholders had hoped.

He added: "It won't be revisiting the dark days of 2012 in a hurry but 2014 has provided something of a reminder as to just how volatile an industry leisure travel can be and Ms Green's exit perhaps serves to remind us that smooth marketing needs to be overlaid with real work on the fundamentals."