UPDATE 1-Britain's Ocado sees sales growth edge lower in latest quarter

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LONDON, Dec 12 (Reuters) - British online supermarket Ocado said on Thursday retail revenue growth slightly slowed in its latest quarter, as it saw growth in weekly orders but it was held back by flat order size.

For the 13 weeks to Dec. 1, its fiscal fourth quarter, Ocado Retail's revenue rose 10.8% to 429.1 million pounds ($550.5 million). That was in line with company guidance but down from third quarter growth of 11.4%.

Average orders per week rose 10.4% to 350,000, while average order size was flat at 104.9 pounds.

Ocado Retail is now a joint venture between Ocado and Marks & Spencer. Their deal, completed in August, signalled the end of Ocado's supply contract with upmarket supermarket chain Waitrose in September 2020 and the start of M&S' first grocery home delivery service.

The joint venture has carried out a product range review. Ocado said it confirmed that M&S has substitutes "at the same price or lower, and of the same quality or better", for the majority of those currently supplied by Waitrose, which represent just over 4,000 products out of the current total range of over 55,000.

Ocado said it anticipated adding many more additional M&S lines to the range.

While Ocado Retail currently has only a 1.4% share of Britain's grocery market, according to the latest industry data, its state-of-the-art technology has enabled it to win partnership deals with supermarket groups around the world, including Kroger in the United States, Casino in France and most recently Aeon in Japan.

Those technology deals have driven Ocado's 8.34 billion pound stock market valuation.

Shares in Ocado were up 2.4% at 0804 GMT, extending gains this year to 55%.

($1 = 0.7794 pounds) (Reporting by James Davey; editing by Sarah Young)