UK Uncut has no offices and no formal leader, and key members often plot strategy over midnight pints of ale in London pubs.

Yet, with more than 60,000 Twitter followers and a sprawling network of college-educated volunteers, the Occupy Wall Street-style group has helped galvanize public opposition to corporate tax avoidance. It has demonstrated inside Starbucks Corp. coffee shops, sued Britain's tax collection agency over a deal with Goldman Sachs Group Inc. and shut down London's Westminster Bridge. It plans to target this month's summit of the Group of Eight, the world's eight wealthiest countries.

"Everywhere that's facing austerity there's been anger about the apparent unfairness of some companies or individuals not paying taxes," said Alex Cobham, a research fellow at the Center for Global Development in London and the author of several studies on tax avoidance. "The difference in the U.K. is that UK Uncut crystallized it and put what people were feeling onto the front pages."