Think tank the Resolution Foundation said the number of multiple home owners grew by 30% between 2002 and 2014.
That figure includes buy-to-let landlords - counted as one owner even if they have multiple properties - as well as those who own separate properties to live in themselves.
At the other end of the scale, four in 10 adults own no property at all.
The foundation said the number of people without property had also risen over the 12-year period.
As a result, the study concluded that there was a growing gap between those who have property wealth and those who do not.
The government is already ploughing Â£60m a year into rural and coastal communities that are most affected by second home ownership, such as Cornwall and Cumbria.
The money - raised from the Stamp Duty surcharge - supports first-time buyers.
Those most likely to own a second home are baby-boomers, currently aged between 52 and 71. They  also typically live in the south of England.
"Contrary to the popular narrative, these second-home owners are rarely your typical middle-income worker shoring up savings, or ordinary retirees boosting pension income," said Laura Gardiner, senior policy analyst at the Resolution Foundation.
"They tend to be baby boomers who are very wealthy indeed relative to their peers, living in the south and east of England."
Those born since 1981 own just 3% of second homes, according to the report.
Since April 2016 those buying second homes have been subject to higher rates of Stamp Duty in England and Wales, and higher Land and Buildings Transaction Tax (LBTT) in Scotland.
In addition, landlords are no longer able to claim tax relief on all their mortgage payments. This change is being phased in between April 2017 and 2020.
It is not yet known to what extent such changes have led landlords to sell up.
Despite those clamp-downs, the Resolution Foundation would like the government to do more to end the property wealth gap.
"Policy makers should consider what more can be done to ensure that home ownership doesn't become the preserve of the wealthy for generations to come," said Ms Gardiner.
As many as 5.2 million UK adults - or one in 10 - have bought or inherited a second home, according to research.