"If Greece exits (the euro), for the tourism industry it could be very profitable," interim chief executive Sam Weihagen said after the company posted a steep first-half loss on Thursday.

"Most probably holidays to Greece will be more profitable for holidaymakers than they are today and places like Spain could lose competitiveness," he told reporters.

The 171-year-old travel group said summer bookings to Greece from Germany were down around 20 percent year-on-year but that bookings from elsewhere to the crisis-hit nation had held up.

Tourism is a vital source of income for Greece, accounting for about a fifth of gross domestic product. The outcome of an election next month will likely decide whether Greece remains in the euro.

Debt-laden Thomas Cook posted a pretax loss of 328.3 million pounds ($510 million) for the six months to the end of March, some 40 percent wider than the loss it reported in the same period a year ago. Its revenues rose 2.4 percent to 3.51 billion pounds.

The company, which had already revealed losses of 263 million pounds for the winter season, secured a 1.4 billion pound ($2.2 billion) rescue package from its lenders earlier this month. It said on Thursday its turnaround plans were making good progress and that bookings had picked up in recent months.

The tour operator has been hit hard by tough trading conditions, especially in Britain where its core customer base of families with young children has been particularly affected by the economic downturn. It has also been hit by unrest in popular destinations such as Egypt, Tunisia and Morocco.

The world's oldest travel group continues to expect this year to be challenging given the economic backdrop and difficult trading environment, particularly in North America and France. It said its full-year performance would be dependent on how well it performs in the late bookings market.

Thomas Cook shares, which have lost around 90 percent of their value in the last year, were 11.11 percent down at 18 pence by 0913 GMT, valuing the business at around 170 million pounds.

"Thomas Cook's results reflect higher seasonal losses from acquisitions and underperforming regions. The future of the group had been questioned in 2011, but we were confident of its survival, hence our 'buy'," said Investec analyst James Hollins.

The company said year-on-year UK bookings were up 5 percent over the last four weeks but that demand from British corporate clients for Olympics packages had been weaker than expected.

"UK corporations are less interested in buying our Olympics packages, maybe their profits are stretched or they think they shouldn't be buying these," said Weihagen.

"We're transferring a lot of them to regular customers and there is huge demand."

Thomas Cook has made a series of disposals in recent months to reduce its 890 million pounds debt. Earlier this week shareholders overwhelmingly backed the disposal of five Spanish hotels and the sale and leaseback of part of its aircraft fleet.

It also sold its Indian business to Fairfax Financial (FFH.TO) for around $150 million this month.

The company, which last week said travel industry outsider Harriet Green would become its new chief executive, said the sales would help it to "re-energize the business and begin to rebuild profitability and reduce debt".

TUI Travel (TT.L), the world's biggest tour operator, recently predicted a strong performance in the key summer trading period with booking volumes well ahead of last year.

($1 = 0.6438 British pounds)

(Editing by Adveith Nair and Hans-Juergen Peters)

• A Permanent Economic Emergency