In the latest PR coup for the Minister without Portfolio, Peter Mandelson is to be the first member of the Blair inner circle to gain admittance to the NPG since the general election.
The arrival of the minister's second photographic portrait - the first appeared in 1988 - comes before that of the Prime Minister and Cabinet heavyweights such as Gordon Brown, John Prescott and Robin Cook.
Charles Saumarez Smith, the director of the NPG, said a number of artists were under discussion for the proposed Blair portrait. Insiders are strongly tipping the sculptor, Nicola Hicks, the daughter of painter Philip Hicks and the sculptor Jill Tweed, who has won critical acclaim sculpting straw and plaster into living forms.
Her grandmother, Kathleen Tweed made pastel drawings of children, including those of the Royal Family.
Last night, Downing Street said any portrait of Mr Blair was still "very much under discussion".
The latest Mandelson purchase, a photograph taken by Polly Borland, will join the ranks of Clare Short, the controversial Minister for Overseas Development, backbencher Tony Benn and Chris Smith, the Heritage Secretary, who were already in place before 1 May as celebrated figures of the Opposition. A ceramic sculpture of the Transport Minister, Glenda Jackson, portraying her simultaneously as Gudrun in Women in Love, one of her Oscar-winning roles, and as a Labour MP, is also on display at the gallery.
The post-victory Mandelson portrait is in marked contrast with the gallery's earlier one - that of the mustachioed Campaigns and Communications Director, photographed by Steve Speller in 1988 holding a single red rose. The youthful eagerness of the party's rising star, clutching the symbol of Labour's modernisation, has been replaced by a knowing, clean-shaven politician, hands folded regally across his lap.
Borland, an Australian photographer who came to Britain in 1989 and who is known for strong, confrontational portraits in harsh colour, uses a striking red background which gives the Prince of Darkness a mildly vampiric aura.
The last leading political figure to be commissioned by the gallery, which was established in 1856 to act as a record of some of the nation's most powerful figures, was John Major, painted by John Wonnacott. He takes a wide-angled view of the former prime minister with one hairy hand shooting forward, larger than his head.
Elsewhere in the gallery, Lady Thatcher is also captured for posterity in an alarming picture by the photographer Helmut Newton, taken after she had fallen from power.
Mr Saumarez Smith says Borland's portrait of Mandelson was acquired in line with the Gallery's policy of "reflecting British public life in all spheres". It was not, however, to be confused with portraits which appear in the gallery's permanent collection of 6,500 pictures.
Portraits in the permanent collection have to be voted on by the Board of Trustees, which comprise the Prime Minister and 14 of his or her appointees and which currently include John Tusa, the managing director of the Barbican Centre, and Max Hastings, editor of the London Evening Standard.
Mr Mandelson is to inhabit the gallery's less prestigious photographic collection of about 250,000 photographs, although Mr Saumarez Smith still described the portrait as "an important acquisition".
Portraits are bought in or commissioned at the artist's "going rate". The gallery's criteria for accepting and commissioning portraits remains the same as in 1856 when, in a spirit of high Victorian enquiry into public figures of the past, Parliament agreed a sum of pounds 2,000 to establish a "British Historical Portrait Gallery". The intention was to establish a historical archive rather than a home for artistic excellence.
The gallery's first acquisition was William Shakespeare, offered to the nation by Lord Ellesmere, who was then a former trustee of the National Gallery. It was hung in temporary accommodation at 29 George Street, Westminster, until a permanent home for the collection was built adjacent to the National Gallery at Trafalgar Square, which was famously described by the author, Henry James, as "like a bustle attached to the cladding of the National's posterior".
Despite this fiercely independent criteria, the problem facing the 1990s curators remains the same as that which beset their Victorian predecessors. "All the political parties think there are too many pictures of politicians from the other parties," says a gallery official. "So getting the chief government spin doctor in early was probably a good move."