LONDON (Reuters) - TUI Travel (>> TUI Travel PLC), the world's largest tour operator, said it was experiencing its strongest summer booking season in six years, boosted by demand from British and Nordic holidaymakers, and said it was confident of beating previous profit forecasts.

The company, formed in 2007 through a merger between First Choice Holidays and the Thomson tourism unit of German group TUI (>> TUI AG), said on Friday it had already sold 58 percent of its overall mainstream summer programme.

A wet and wintry start to the year and a tough economic climate across Europe has driven up demand for TUI Travel's fixed-price package holidays for cash-strapped travellers.

The company has also seen good appetite for tailored holidays that allow holidaymakers to pick options such as adult-only hotels.

"This is the strongest sales position we've had since the merger," Chief Executive Peter Long said.

"Our customers regard the overseas holiday as sacrosanct, particularly in the UK and this year is no different. What we're seeing is our customers reprioritising their discretionary spend and the summer holiday comes right at the top of the list."

Summer 2013 sales in Britain and the Nordics were up 13 and 14 percent respectively compared to the year before, offsetting a 13 percent decline in France, where the company is reducing capacity.

"Given current trading and the visibility we have within our businesses we anticipate full-year underlying operating profit growth of at least 10 percent on a constant currency basis," Long said.

This compares to a company forecast in March for underlying operating profit growth at the top end of its guidance of 7-10 percent.

The company posted an underlying operating loss of 289 million pounds for the six months to the end of March, compared to a loss of 317 million pounds a year earlier, citing a strong 2012/13 winter season which closed ahead of its expectations.

Tour operators and airlines tend to report losses in the traditionally weaker first half of the year and make the bulk of profits over the summer months.

The company increased its interim dividend by 10 percent to 3.75 pence per share.

Panmure Gordon analysts said the company's guidance was "encouraging" and increased their target price to 315 pence from 303 pence, although they said that trading could get tougher, particularly in Britain as the weather improves.

Shares in TUI Travel, which have risen 21 percent since the start of the year to trade at a forward price-to-earnings ratio of 11.6 times compared to 12.9 times at rival Thomas Cook (>> Thomas Cook Group plc), were up 2.1 percent at 347.9 pence at 9:39 a.m.

(Reporting by Brenda Goh; Editing by James Davey and Tom Pfeiffer)

By Brenda Goh

Stocks treated in this article : Thomas Cook Group plc, TUI Travel PLC, TUI AG