* U.S import most popular in Britain
* UK spending forecast to rise 3.8 pct
* Event gaining popularity in Germany, Spain, Italy (Adds detail, Barclaycard, John Lewis, Dixons, Greece, Denmark comments)
LONDON, Nov 24 (Reuters) - Retailers across Europe chased shoppers on "Black Friday" in a test of consumer demand, particularly in Britain where the spending spree imported from the U.S. has become a particular feature.
After last month suffering their biggest decline in sales volumes for four-and-a-half years, British retailers are pinning their hopes on discounts to get shoppers, who are being squeezed by inflation and subdued wages growth, spending again.
In Britain the annual promotional event, which has previously focused on electrical goods, has been mainly played out online since 2014 when it was marred by scuffles in stores.
The jury also remains out on whether retailers make money by cutting prices in an event which was imported to Britain from the United States by online retailer Amazon in 2010.
British retailers reported strong early demand.
Barclaycard, which processes nearly half of all UK debit and credit card transactions, had by 1000 GMT seen a 3 percent increase in spending compared to Black Friday last year and a 29 percent increase in transactions.
Department store John Lewis said 0700-0800 GMT was the busiest shopping hour, with an average of 495 units ordered per minute and the top seller by value a LG Smart TV for 1,399 pounds ($1,864).
"It will be our busiest trading day of the year," John Rogers, chief executive of electricals to toys retailer Argos, which is owned by Britain's second biggest retailer Sainsbury's , told Reuters.
Research firm GlobalData forecasts UK spending during the Black Friday period - Monday Nov. 20 to Monday Nov. 27 - will grow by 3.8 percent year on year to 10.1 billion pounds.
PROFITABLE OR DAMAGING?
Black Friday's advocates argue carefully planned, targeted promotions with global suppliers give them a sales boost, while still maintaining profit margins.
Critics say the discounts drag forward Christmas sales that retailers would otherwise have made at full price and can dampen business in subsequent weeks.
Seb James, CEO of Dixons Carphone told BBC radio the company gains market share through Black Friday, rather than just pulling sales forward.
Like last year, retailers including Amazon and market leader Tesco, are stretching promotions by up to two weeks, hoping to smooth out demand and reduce pressure on supply and distribution networks.
Black Friday, the day after the U.S. Thanksgiving holiday, was so named because spending would surge and retailers would traditionally begin to turn a profit for the year, moving from the red into the black.
Its impact is also being felt across the continent.
In Germany sales promotions on Black Friday and Cyber Monday (Nov. 27) are expected to add around 1.7 billion euros ($2 billion) to retailers' revenues, about on par with 2016, a survey by trade body HDE found.
About 8 million France-based consumers are expected to shop from Friday to Monday, translating into expected revenue of around 945 million euros, according to a study conducted by Kantar TNS for U.S e-commerce firm eBay.
In Denmark supermarket chains Bilka and Fotex said their websites had been taken down by cyber attacks at the launch of their Black Friday campaigns.
Black Friday has also been growing in Italy. This year all major retail chains are advertising discounts. Signature department store La Rinascente is open until midnight on Friday and is advertising discounts of up to 50 percent.
It was more subdued in Greece, where the economy has contracted by more than a quarter between 2008 and 2016.
"People dont have money to spend," 32-year old Athens shopper George Christopoulos told Reuters. ($1 = 0.7506 pounds) ($1 = 0.8435 euros) (Additional reporting by Maria Sheahan in Frankfurt, Matthias Blamont in Paris, Valentina Za in Milan, Lefteris Papadimas in Athens and Jacob Gronholt-Pedersen in Copenhagen; editing by Alexander Smith and Keith Weir)