Less than half of Britons now regard themselves as primarily British with the largest rise in a separate national identity occurring among the English, a major report said today.

The key finding by the National Centre for Social Research (NatCen) is bound to fuel the debate about nationalism, particularly in the run-up to the Scottish parliamentary elections.

Over the past 10 years, particularly in the light of devolution, the decline of a British national identity has been most marked among the English, noted the report. Less than half the population of England now regards itself as British when "forced to choose" between national identities of being English or British.

The institute found how in 1996, the year before Labour came to power, 52% of Britons put their "best or only national identity" as British. However, further polling showed that by 2005 this had fallen to 44%.

The most recent marked decline in feeling British has been among the English. According to NatCen, when people living in England were asked to make a "forced choice" about their national identity, in 1992 some 63% described themselves as British but by 2005 this fell to 48%, a reduction of 15%.

David Cairns, Deputy Scottish Secretary, said: "It's a daft question. The strength of the UK is that you can be both."

Alex Salmond, SNP leader, said: "We are seeing a resurgent Scottish identity and an emergent English identity and both are extremely positive things."

Elsewhere in the report, there is overwhelming support for voluntary euthanasia for terminally ill patients, with eight out of 10 people in Britain favouring the right of people to take their own lives in such circumstances.