There was a five-fold increase in people born in the UK holding both British and EU passports, the analysis of Census 2021 figures showed.
While the change has been partly driven by migration over the decade, with more people moving to the UK from the EU, it is also thought more people have taken up additional passports after Brexit, the Office for National Statistics (ONS) said.
In 2021, a total of 1.26 million usual residents of England and Wales held multiple passports (2.1%), up from 612,000 (1.1%) in 2011.
The majority – 84.4% or 50.3 million – of usual residents across the two nations held only one passport in 2021.
While the number of UK/EU passports held increased by five times over the 10-year period for UK-born residents, there had been a three-fold rise for non-UK-born residents since 2011.
There was also a six-fold increase in UK-born residents holding both British and Irish passports
Jay Lindop, from the ONS, said: “The number of people with dual citizenship has doubled since 2011, with more than 1.2 million usual residents in England and Wales now holding multiple passports.
“This change has been partly driven by migration over the decade, with an increase in people moving here from the EU. As people who have settled in England and Wales go on to have children, we can see an increase in dual citizenship among the younger ages.
“The rise in dual citizens may also suggest greater uptake of additional passports following the end of free movement when the UK left the European Union.”
There were age differences among dual citizens, with the rise in UK-born British and European dual citizens driven by younger age groups, but British/Irish passport holders being older, the ONS said.
More than half (58.7% ) of dual citizens born in the UK and holding both UK and EU passports were aged under 16, while just over a third (36.7%) of UK and non-EU dual citizens were under 16.
UK/EU dual citizens had a median age of 12, while for EU-only passport holders it was eight-years-old on average.
Non-EU dual citizens had a median age of 22, and UK/Irish dual citizens were older, with a median age of 47.
For Irish-only passport holders, the median age was 33.
A rise in UK/Irish dual citizens across the decade was most apparent in those aged 50 to 70-years-old, the ONS said, adding that this suggested many only took up their dual nationality more recently despite moving to England and Wales years ago.
The top five UK/EU passports for UK-born dual citizens were primarily held by children or young adults, with Ireland having the only older population, the ONS said.
For UK/French and UK/German passport holders the median age was 15, for UK/Polish it was seven and for UK/Italian it was 20.
The five most common non-EU passports for UK-born dual citizens showed a wider variety of average ages, with UK-Australian having a median age of 39, UK-US being 21, UK-Nigerian was 19, UK-Canadian was 36, and UK-New Zealand was 28.
The ONS said the young ages of most UK/other dual citizens suggested they were the children of first-generation migrants.
The statistics body said the reasons for holding multiple passports were likely to differ between those who held a UK passport first and those who held a non-UK passport first, noting that the census did not collect data on when passports were acquired.
Looking more closely at the areas where dual citizens are based in the two nations, the ONS found that more than a third (39.1%) of all UK-born holders of UK and EU passports in England and Wales were living in London at the time of the 2021 census.
Around a fifth were based in the South East (20.3%).
These figures are well above all other regions, with the North East accounting for only 1.4% of the total.
It was a similar picture for UK-born holders of UK and non-EU passports, with just over a third (34.7%) based in London and a fifth in the South East (20.2%), while only 1.9% were in the North East.
Meanwhile, nearly one in 10 (9.6%) UK-born residents in the London borough of Kensington & Chelsea were dual passport holders – the highest percentage for any local authority in England and Wales and up from 5.4% in 2011.
Westminster & the City of London had the next highest proportion (7.2%), followed by the London boroughs of Hammersmith & Fulham (7.1%) and Camden (7.0%).
Cambridge had the highest percentage outside London (5.5%), followed by Oxford (5.0%) and Elmbridge in Surrey (4.0%).
Of the top 50 local authorities with the highest proportion of UK-born residents who were dual passport holders, only four were outside south-east England: Bristol, Cambridge, Exeter and South Cambridgeshire.
By contrast, 11 of the top 50 areas with the highest proportion of non-UK-born dual citizens were outside the South East, including Craven in North Yorkshire, Bath & North East Somerset and High Peak in Derbyshire.
Sevenoaks in Kent topped this list (16.1%), followed by Elmbridge (15.7%) and then Richmond-upon-Thames in London and Waverley in Surrey (both 14.5%).
In Wales, Cardiff had the highest proportion of UK-born residents who are dual passport holders (1.1%), followed by Monmouthshire and Ceredigion (both 0.7%).
Monmouthshire had the highest figure for non-UK-born residents with multiple passports (9.7%), followed by Vale of Glamorgan (8.5%) and Conwy (8.2%).