Wm Morrisons (MRWSY)  shares were one of the top gainers in London Thursday after the U.K.'s fourth largest supermarket reported a fourth consecutive quarter of same-store sales grow on lower prices and good Halloween trading.

Like-for-like sales, excluding fuel, were up 1.6% in the three months ending October 30, the company said, while same-store sales were up 2% and 0.7% in the second and first quarters respectively. Total sales, excluding fuel, were down 1.2% due to the impact of store closures and the exit of convenience stores.

Shares in the group rose 1.4% by mid-morning in London, changing hands at 224.4 pence each, extending their six month gains to 17.6%.

Halloween sales, a relatively new phenomena in the U.K., were up 20% year-on-year, the company said, making it the biggest year ever. Morrisons said it is becoming more relevant around key seasons and events.

However, life in the grocery aisle is not sweet on the British Isles as pressure from low-cost competitors continues and the pound's rapid decline forces up food prices. Hargreaves Lansdown analyst George Salmon said the upcoming holiday season will be crucial for the supermarket chain.

"Morrison's strong balance sheet has given them the power to invest in improving its shops and lowering prices, and so far customers are responding well," he said. "Transaction numbers show good momentum, and record seasonal sales mean that the Halloween proved to be of a treat."

"This certainly bodes well for Morrison, but, with the other main supermarkets raising their games too, the festive period will prove to be the real test," he added.

Growth in sales at Morrison's comes at odds with Walmart's (WMT) U.K. unit, Asda, which has seen sales decrease significantly over the past quarters (7.5% in the second quarter) and has steadily lost market share.

Morrisons also said prices fell throughout the quarter, with deflation of 1% amid a fierce price war between country's 'Big 4' supermarkets - Tesco (TSCDY) , Sainsburys (JSAIY) and Asda and Morrisons.

According to data from Kantar Worldpanel Tesco's market share was 28.2% for the 12 weeks ending October 9, while Sainsbury's stood at 16%, Asda at 15.6% and Morrisons at 10.4%.

There is also growing competition from low-cost European chains Aldi and Lidl, whose market shares continue to increase. Aldi's grasp on the market grew to 6.2% and b edged up to 4.6% of the total market.

The 'Big 4' chains have been lowering prices in an attempt to fend off the new entrants, however this strategy is now under pressure.

Britain's supermarkets may be embroiled in an aggressive pricing war, but the 19% fall in the pound since the U.K. voted to leave the European Union on June is expected to provide a difficult landscape in the market as food-price inflation accelerates.

Britain's Office for National Statistics estimated last month that September's consumer price index rose to an annual rate of 1%, the fastest pace since November 2014.

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