The deal had been expected since people close to the process said last week Suntory - best known for beer and Yamazaki whisky - was in advanced talks on a purchase that would pre-empt an auction of the British drinks.

Japan's second-largest drinks maker by sales after the local arm of Coca-Cola Co has plenty of cash after raising $4 billion in a stock market flotation in June. It was always seen as the most likely buyer for the brands after GSK announced plans for their disposal in April.

The energy and blackcurrant drinks are popular in Britain but from GSK's point of view lack global reach, especially in the big emerging markets that are becoming the focus of the British drugmaker's consumer health business.

For Suntory, however, they offer a growth opportunity to counter sluggish demand at home.

One person at a private equity firm which had considered a rival bid said Suntory was paying "a very hefty price", explaining GSK's willingness to allow it to pre-empt an auction.

Lucozade and Ribena, introduced in 1927 and 1937 respectively, have combined annual sales of just over 500 million pounds, putting the transaction on a multiple of 2.7 times revenue - at the high end of recent soft drinks deals, which have tended to be in the 1.5 to just over 2 times area.

Suntory bought the Orangina Schweppes drinks brand for more than $3 billion in 2009, giving it a significant presence in France and Spain. By acquiring a new business with a focus on Britain, Suntory said it expected to further increase sales.

The purchase also extends its reach into countries such as Nigeria and Malaysia.

Suntory Beverage President Nobuhiro Torii said the price was justified because the chance to buy the brands was "an extremely rare opportunity" and there was scope for cost savings in both logistics and procurement.

"Considering synergies and such, this is not at all an expensive purchase. I wouldn't say it's cheap, but it's not expensive. Our management will be tested by how much we can achieve in synergies," he told reporters.

LONG-TERM POSITIVE

Industry analysts said the price was high but the drinks added strong brands and distribution channels that could be used with Orangina to enter emerging markets.

Moody's Investors Service said in a note written before the deal was unveiled that it viewed the expected acquisition as a long-term positive for the Japanese company.

"One of Suntory's main rating constraints has been its geographic concentration as about 80 percent of sales comes from domestic sources. Acquiring these UK brands will improve its geographic diversification," the ratings agency said.

Suntory said the deal would have a limited effect on its 2013 results and it was examining the effect it will have on its outlook for the following business year and beyond.

The sale is expected to be completed by the end of the year, subject to regulatory approvals.

For GSK, it will yield net proceeds of around 1.3 billion pounds after tax, fees and costs, which will be used to reduce debt and for general corporate purposes. That may disappoint some investors who had hoped GSK might use the proceeds to pay a special dividend.

The net gain will be excluded from 2013 core operating profit and earnings per share.

A GSK spokesman said Suntory's bid was also attractive because it would protect jobs in Britain. Some 700 employees will transfer to the Japanese group, including around 500 workers at GSK's Coleford factory in the west of England.

The spokesman said there was expected to be very little, if any, impact on jobs as a result of the sale.

Other potential buyers who had been eyeing Lucozade and Ribena included Blackstone, Lion Capital, Cinven, CVC Capital Partners and KKR.

JP Morgan and Greenhill acted for GSK on the disposal, while Morgan Stanley advised Suntory.

Lucozade and Ribena are the latest in a series of venerable British food brands to be bought by foreign buyers. Other deals include last year's purchases of breakfast cereal Weetabix by China's Bright Food and Branston pickles by Japan's Mizkan Group, as well as the 2010 sale of chocolate maker Cadbury to Kraft Foods Group Inc.

($1 = 0.6398 British pounds)

(Additional reporting by Anjuli Davies; Editing by Louise Heavens and David Holmes)

By Ben Hirschler and Ritsuko Shimizu