The gallery already has three regional outposts

But much of the collection is not on show at any one time.

The Durham project would provide an outlet for the gallery's large collection of 20th century work.

"It is something we've been looking into for a while - we already have regional partnerships where we show some of our collection," a National Portrait Gallery spokeswoman told BBC News Online.

The gallery's partnership collections at present are Montacute House in Somerset, Beningborough Hall in Yorkshire and Bodelwyddan Castle in Denbighshire, north Wales.

The gallery is said to have considered Middlesbrough for its northern outpost but Durham, with its cathedral and castle, has the advantage of having been declared a world heritage site.

"We are looking for a venue in Durham but it's early days, and we are still at the stage of feasibility studies."

"But we are still looking for somewhere to show parts of our 20th century collection," said the spokeswoman.

Access

The gallery's staff and trustees are working with Durham University and the city on possible locations for the collection.

The Government has stressed the need for the great national collections to try to widen access to a broader cross-section of the population.

A number of collections, both national and regional, have been opening galleries around the UK.

Walsall now has a lottery-funded art gallery, while the Walker Art Gallery in Liverpool opened this month after a £4.2m refurbishment.

Manchester Art Gallery is set to reopen in May after a £45m revamp and later in 2002 the Baltic, an international centre for contemporary art, will open in Gateshead - just 20 miles from Durham.