This represented 17.9% of households and was a fall of 0.8 percentage points, or 153,000 households, on a year earlier, the second consecutive fall.
In all, 1.8 million children lived in these households, as did 5 million people aged 16-64.
Sickness, both long-term and temporary, was the main reason given for not working by those people aged 16 to 64 living in workless households, accounting for 1.45 million, or around three in every 10 workless people.
The second most common reason given was being unemployed, accounting for 1.03 million, or one in five. The next three most common reasons were looking after the family, retirement and study.
Some of the workless people aged 16 to 64 give study or retirement as their reason for not working. If fully retired and student households are removed, the number of households in the UK that are workless is 2.92 million.
Xenios Thrasyvoulou, founder and MD of PeoplePerHour, said: "One of our biggest growth areas are people who are out of work and seeking to get back into full-time employment.
"For many people who lose their jobs, but are keen to work again, the most disheartening and demoralising aspect of being out of work is sending out hundreds and hundreds of CVs, only to receive rejection after rejection. The problem is that they are having to compete against hundreds of other candidates for the few jobs that are out there.
"What we have seen is an increasing number of highly skilled people, who are unemployed for whatever reason, who are able to offer specific skillsets to small businesses. And in the current unpredictable economic environment, small businesses are more comfortable taking on skilled staff on a freelance basis, than recruiting full-time staff."
As well as a fall in workless households, there was also a fall of 36,000 in working households – those with at least one person aged 16 to 64 where all adult members are in work. In April to June 2012, there were 10.9 million such households, representing 53% of all households.
There was a rise of 246,000 in mixed households – those that contain some people in work and some who are not. The number of mixed households stood at 5.97 million, or 29.1% of the total.
Since 1996, the earliest point a consistent series is available, the lowest estimate for both the number and percentage of workless households was in 2006, two years before the economic downturn hit the UK in 2008. The number of workless households was 233,000 lower than in 2012, at 3.4 million, and the percentage was 0.6 percentage points lower than in 2012, at 17.3%.
The ONS reports over the past 15 years there has been a fall in the percentage of lone parent households with dependent children that are workless, from 51.9% in 1996 to 37% in 2012.
The first part of this fall happened between 1996 and 2006, the proportion then remained flat for a few years but fell by 2.2 percentage points between 2011 and 2012.
Comparing lone parents and couple households, the latter have a much lower chance of being a workless household. In 2012, around 4.9% of couple households with dependent children were workless, much lower than the 37% for lone parent households, reflecting the ability for couple households to share childcare responsibilities.
Another important factor is the age of the youngest child in the family, as this has an impact on the ability of parents to go out to work. As children get older, it becomes easier for those responsible for looking after them to go out to work.
The impact is much greater for lone parents, as they are generally the sole carer for the child. In 2012, 59% of lone parent households with their youngest child aged 0 to 4 were workless.
However, when the youngest child was aged between 5 and 10, the percentage of lone parent workless households was 35%.