UPDATE 1-Aldi UK's record Christmas driven by premium product demand

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LONDON, Jan 4 (Reuters) - Aldi UK, the British arm of the German discount supermarket, said its sales rose over 15 percent in December year-on-year, indicating it continued to win market share from bigger rivals.

The firm said on Thursday its record Christmas performance was boosted by strong demand for its premium ranges and pushed total sales in the UK and Ireland during 2017 beyond the 10 billion pound ($13.5 billion) barrier for the first time.

Aldi, along with fellow German discounter Lidl, has been winning UK market share from Britain's big four grocers - market leader Tesco, Sainsbury's, Asda and Morrisons.

In contrast to Britain's traditional big four grocers, Aldi and Lidl are continuing to aggressively add space.

Industry data published in December put Aldi's UK grocery market share at 6.9 percent, up 0.7 percentage points on the year, making it Britain's fifth largest grocer.

Aldi UK said it saw a surge in demand for its premium "Specially Selected" products, with sales increasing by over 30 percent during December. It said top-selling premium products included Aberdeen Angus beef roasting joints and Irish cream liqueur.

"Although we saw strong growth across all categories, the performance of our premium Specially Selected range in particular surpassed all expectations," said Aldi UK & Ireland Chief Executive Matthew Barnes.

Aldi UK also said on Thursday it would pay its store assistants a minimum of 8.85 pounds an hour from Feb. 1 - matching the rate recommended by campaigning group Living Wage Foundation. ($1 = 0.7399 pounds) (Reporting by James Davey; Editing by Susan Fenton and Kate Holton)