Britain's blue-chip companies have reduced their average tax rate by almost a third over the last two years, according research from accountancy firm UHY Hacker Young.

This year companies in the FTSE 100 share index paid 26 percent of their profits in tax, down from 35.8 percent in 2009 and 30.1 percent in 2010.

The lower tax rate partially reflects a reduction in the headline corporate tax rate to 26 percent from 28 percent in the UK, but the research found it was also caused by some British companies moving their headquarters overseas.

UHY also noted that companies in the FTSE 100, which is increasingly dominated by foreign mining firms, were generating a higher percentage of their revenues overseas where tax rates are often lower.

With more of companies' operations now based overseas it is only sensible for them to ensure that their business is structured properly so that they are paying tax at the best rate, said Roy Maugham, tax partner at UHY Hacker Young.

The same FTSE 100 companies attracted criticism on Friday after a study showed pay for Britain's top directors rose almost 50 percent last year.

(Reporting by Sarah Young; Editing by Greg Mahlich)