The increase comes as the average house price has rocketed by 45 per cent over the same period.
Meanwhile, the study warned that if current trends continue, narly half a million more young adults could still be living with their parents in ten years time, according to the study published today by Aviva.
The report said the number of adults aged 25 to 34 who live with their parents has already grown from 903,000 to around 1.23 million.
If this trend continues, it said the UK could see a further 452,000 people aged 25 to 34 living with parents by 2026, following an analysis of Office for National Statistics (ONS) data from 2016.
Aviva said the growing trend of multi-generational living comes as the average price paid for a first-time property rose from £146,000 to £211,000.
A survey by Aviva of 500 young adults who still live in the home they grew up in found one in 12 do not ever expect to fly the nest. On average, those who do expect to move out at some point believe they will be aged around 28 years old when this happens.
When asked how they felt about their current living situation, 47 per cent of adults living with parents said they were “very happy”. But happiness with their situation appeared to diminish for the over-30s, with less than a third of people aged 30 to 34 who still live with their parents saying they were very happy with their circumstances.
Lindsey Rix, managing director of personal lines at Aviva UK, said: “The challenges of getting on the property ladder are well publicised, but it’s startling to see that one in three adults who live with parents expect never to own a property and further fifth believe the only way they will own a home is by inheriting one.
“However there is good news too, as the majority of ‘children’ in this situation are happy with this set-up, so in many cases there may be no desire to leave. If house prices continue to rise at their current rate, we can expect the proportion of adult children living with parents to grow even further.”
Nearly two thirds of adult children living with parents said they could not afford to move out, while 48 per cent said they live with family to save money.
Meanwhile, nearly a quarter of adult children living in the family home said they liked being “looked after”, while one in seven said they are looking after their parents. One in 10 were scared of moving out.