Pride in Britain has fallen sharply over the course of a generation.
The percentage of people declaring themselves "very proud" of Britain fell from 55% in 1981 to just 45% today.
The main reason is generational, with younger people less likely to have the "strong attachment" to Britain of older generations, said the researchers.
The finding came a study sponsored by the Economic and Social Research Council.
It said the generational change had been more rapid in Wales and Scotland than in England, suggesting that young people may become potentially more receptive to appeals from nationalist parties.
The study, by the National Centre for Social Research, involved investigators from several universities examining attitudes to national identity in the wake of devolution for Scotland and Wales in 1999.
The study found that Britishness provided an "inclusive" identity.
"Just as members of minority communities define themselves as Black British or Asian British, people from the white majority tend to emphasise their Britishness when they move from their home territory to a different one," said the researches.
Devolution appears to have affected the way English people think of themselves, with the proportion who think of themselves as English rising from 31% in 1992 to 39% in 2003 - and peaking at 44% with devolution in 1999.
"Senses of British identity and pride in Britain were strongest in England," said the researchers. "In Wales, and even more so in Scotland, substantial minorities did not feel British at all. But although overall levels of Britishness are much lower in Scotland and Wales than in England the extent of changes over time have been rather modest, and appear to be part of longer-term trends rather than specifically affected by devolution."
