John Donne became the Dean of St Paul's

The public gave �200,000 towards the �1.4m needed to acquire the portrait, which was created in about 1595 by an unknown artist.

The National Heritage Memorial Fund and the Art Fund also gave grants.

The gallery is just �500 short and hopes visitors will make up this amount over the bank holiday weekend.

"It's absolutely right, but also wonderful, that this very important picture has been bought by the National Portrait Gallery, where the wide world can enjoy and admire it," said poet laureate Andrew Motion, who backed the campaign.

Grateful

The painting, regarded as the most important painting of Donne, has been privately owned for 400 years.

Although the artist behind the portrait is not known, it was bequeathed to an ancestor of the current owner in Donne's will.

It depicts Donne, who lived from 1572 to 1631, at around the time he wrote what is considered to be one of his greatest poems, To His Mistress Going To Bed, from his Elegies series.

"The response to the John Donne appeal has been outstanding, and my thanks go to all those who have contributed," said Sandy Nairne, director of the National Portrait Gallery.

The metaphysical poet's other famous works include A Valediction Forbidding Mourning and The Anniversary.