LONDON — British retailer Woolworths has blamed piracy for poor DVD sales over the Christmas period.

CEO Trevor Bish-Jones confirmed that the market for blockbusters “Shrek 2,” “Spider-Man 2” and “Harry Potter and the Prisoner of Azkaban” were nearly halved.

“I think what’s happened is piracy,” he said. “That took the top off those mega-releases.”

The third “Harry Potter” pic, released in November, sold 770,000 units in its first two days, compared with 1.6 million for predecessor “Harry Potter and the Chamber of Secrets.”

“The ‘Harry Potter’ franchise may not be quite as strong as it was, but everything suggested that the latest ‘Harry Potter’ should have flown off the shelves,” said Bish-Jones, blaming “replication plants in China pumping out counterfeits.”

However, the British Video Assn. suggested pricing was as much a factor as piracy, with consumers preferring to buy cheaper catalog DVDs rather than new releases.

British DVD sales increased 10% to 53 million units in December compared with the same period in 2003. But that represents a significant slowdown in the growth rate of the DVD market, after a 46% increase in the first nine months of the year.