Tate Modern, which opened in May 2000 in a former power station on the south bank of the River Thames, looks set to eclipse the National Gallery as Britain's second most popular visitor attraction.
The latest industry figures, based on the financial year ending in April 2012, put the British Museum on top with 5.8 million visitors, followed by the National Gallery with 5.3 million and Tate Modern with 4.9 million.
Tate Modern, which showcases international modern and contemporary art, is part of a group of galleries which includes the Tate Britain, which covers British art from 1500 to the present day and is also in London.
There are also Tate galleries in Liverpool in northwest England and St Ives in southwest England.