MOVE over Charles Darwin and Elizabeth Fry. A leading historian wants to see a black face on a banknote to demonstrate the changing social and ethnic composition of Britain.

Mary Seacole, the nurse who served in the Crimea, Olaudah Equino, an 18th century anti-slavery writer, or Dadabhai Naoroji, the first South Asian MP who sat for Finsbury in the 1890s, have all been suggested as candidates.

Linda Colley, the author of several books on British identity, said in an interview for Fabian Review, the magazine of the Fabian Society, that "practical measures'' were needed to create a new definition of Britishness to include blacks and Asians.

''There are omissions which are painfully obvious and which could easily be put right,'' she said. ''Why, for instance, are all the people on the British banknotes always white?''

While most of the historical figures depicted on the notes are household names, such as Charles Darwin and Sir Edward Elgar, the Fabians - who are organising a major conference on the future of Britishness - are questioning why Sir John Houblon should stay on the pounds 50 note when few have heard of him.

The first governor of the Bank of England, he replaced Sir Christopher Wren in 1994 to commemorate the 300th anniversary of the bank.

Sunder Katwala of the Fabian Society said it was time for a national debate about the identities of new faces.

''Few people know how these things are decided, or how somebody like Sir John Houblon was chosen to be the face of the pounds 50 note,'' he said.

"Our national symbols should reflect the nation that we are today.

"Deciding how we should do that could be a really positive way to capture and increase the growing public interest in our history.

"Just as Florence Nightingale was on the pounds 10 note from 1975 to 1994, Mary Seacole could be a symbol not just of our history but of the diversity which is today at the heart of our most cherished national institution, the NHS.''