The research shows that every UK region is now more affluent than it was five years ago, with measures including household wealth, gross domestic product (GDP), exam results, charitable donations and entrepreneurship taken into account.
Akshaya Bhargava, chief executive of Barclays Wealth and Investment Management, said: "The UK is becoming more prosperous, with every region having grown in affluence since 2010.
"It is also encouraging to see that regions and cities are starting to close the gap with London in terms of prosperity; with the North East, for example, seeing business growth rates behind only London."
London and the South East remain the most prosperous regions, while the capital also boasts the most millionaires – up 48% in the past five years to 191,000, which is more than the combined millionaire population of Wales, Scotland, Northern Ireland and Northern England.
The East of England is ranked third as rising house prices push more wealthy Britons outside of London, with 23,000 more millionaires now calling the East their home.
Reading is listed second for prosperity in the UK, according to the index, with average earnings of £30,562.
Growing numbers of entrepreneurs in the UK is also seen as another factor in increasing wealth, with Cambridge ranking third as it has emerged as a start-up hub.
The North East and Newcastle fall low on the prosperity index. But the study also showed the highest rate of growth in millionaires across the North East, alongside Wales, at a rise of 50% to 12,000 since 2010.
The study said Northern regions "may be on the cusp of change, with the North East leading the way".
Despite the jump in wealthy Britons over the past five years, the research said growth in millionaires is expected to return to more normal levels over the long term, with a 9% increase in the UK expected by 2025, in-line with GDP growth.
Here are the country's wealthiest cities ranked according to the prosperity index: