High street stores around Britain were forced to close their doors to customers on one of the busiest shopping days of the year after activists protesting against tax avoidance by big businesses swarmed inside and caused havoc.
Retailer Topshop's flagship branch in London's Oxford Street was one of a series of shops that fell victim to the co-ordinated protest.
A Sussex Police spokesman said 18 people were arrested during a demonstration in Brighton.
He said that eight demonstrators gained entry to Topshop in Western Road and glued their hands to the inside of the shop windows. A shop worker was assaulted during the demonstration, he said.
The West End protest started at 11am when campaigners from UK Uncut joined together inside Topshop and started blowing whistles and chanting as the store was packed with Christmas shoppers. Many campaigners were forcibly removed from the premises by private security guards and police.
One campaigner, who wished to be known only as Lucy, said: "I am a peaceful protester. A woman was being thrown out of the store and I objected so I was picked up by two private security men. They lifted me by my ankles and my hair. It was quite scary really."
Security guards also removed journalists from the store. One female reporter was carried out by her arms and legs.
A UK Uncut spokesman said they targeted the shop because it was part of Sir Philip Green's Arcadia retail group. Campaigner Stephen Trevelian, 26, from Brighton, said: "Philip Green is a multi-billionaire tax avoider, and yet is regarded by David Cameron as an appropriate man to advise the Government on austerity."
Smaller-scale protests were held in 19 towns and cities - including Liverpool, Glasgow, Edinburgh, Leicester, York, Bristol, Portsmouth, Southampton and Cambridge.
Arcadia group declined to comment on the protests.