Labour and the Conservatives face structural decline unless they grasp the potential of the fast growing minority vote, according to an authoritative new analysis.

A study of demographic patterns, polling data and statistics from the recent European elections indicates that the so-called superdiversity emerging in towns and cities will have a massive impact on future results.

The research, led by Trevor Phillips, the former head of the Equalities and Human Rights Commission, and academic Richard Webber, suggests that two out of three visible minority voters in London endorsed Labour in May's European elections, while the same proportion of white voters backed either the Tories or Ukip.

White voters' support for Ukip matched that of the Tories and was double the number of them backing Labour.

"We may tentatively conclude that the principal factor differentiating London's attitudes from the rest of the country is not its socially liberal attitudes but the size and preference of the visible minority vote within it," the authors say.

Labour traditionally secures about 70% of the visible minority vote. By retaining that loyalty, they could eat into the heartlands of rivals as more minorities move into suburbs and other less urban areas.

But despite that trend – a so-called "browning of Labour" – it risks the security and opportunity of that visible minority support by failing to fully integrate those minorities into the party itself and to reflect their concerns. Its reliance on minority voters would be exacerbated by Scottish independence, the report says.

Dangers also lie in Labour's response to the rise of Ukip. "Even if a policy tilt towards Ukip may benefit Labour in the short term (ie in time for a 2015 general election), there will be a huge price for Mr Miliband and his successors to pay in every subsequent general election for several decades," the authors suggest.

The issue is just as acute for the Tories. The party captured just 16% of the visible minority vote in 2010. Pollster and former party vice-chairman Lord Ashcroft has been a leading voice calling for the party to do more to attract minority voters.

Last weekend, the Guardian obtained a tape of the police minister, Damian Green, privately describing his party's progress in this regard as appalling.

The analysis suggests Tories might seek a multi-faceted approach.

"First, they could employ a race-conscious electoral strategy that would acknowledge that they won't win many more minority votes any time soon, but adopted a less ambitious goal – to shed their image as a party hostile to minorities. In time they might then hope to nibble away at Labour's advantage.

"Second, they could work hard, through boundary changes and planning policy, to corral visible minority voters in a few urban areas – thus concentrating the growing Labour vote in fewer constituencies. Alternatively, they could adopt a more radical strategy by trying to peel off some minority groups."

Similar tactics helped conservative parties in Canada and Germany attract hitherto hostile minority voters. But there would be pain involved.

"To replicate this approach in the UK would involve a major policy U-turn for Mr Cameron: a policy of more immigrants, more ruthlessly selected for educational attainment."

There would also be philosophical problems for a Tory leader. He or she would have to make the party more appealing to minorities without engaging in the so-called identity politics abhorred by the grassroots.