A new report published today by the Scottish Widows think tank Centre for the Modern Family has shown families with grown up offspring living under their roof are spending £1,200 on every day household expenditure compared to parents without.
The authors of the research said the total annual cost of what it called 'full nest syndrome' in the UK was £3.2 billion based on their calculations.
Carolyn Fairbairn, chair of the Centre for the Modern Family, said: "This research highlights the very real pressures being felt by Full Nesters as a result of the rapid emergence of the 'never fledged generation'.
"With many parents raiding their savings or putting their retirement plans on hold to cover the cost of their adult children still living under their roof, we need to ask ourselves what the longer term implications of these trends are and what this means for the financial well-being of these parents."

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A third reported they were contributing less to their savings, while 28% have been spending their savings to meet the cost of everyday living.
Some said they were conscious that this could be compromising plans for later life, with a quarter (24%) saying they wish they were able to focus more on preparing for the future.
The latest figures showed that more than a quarter of adults between 20-34 are still living at home, and 19% of students have been opting to stay at home while studying. This suggested the high cost of living and accommodation means they are unable to "fly the nest" even for a short time, the report stated.
Parents with children at home still may be putting their own financial future at risk, the researchers said.
They found 31% had cut spending on vital items such as groceries, compared to 21% of parents living by themselves.
Some 16% have needed to take out a loan, spent on credit cards, or gone overdrawn, against 7% of empty nesters.
Two thirds said they were financially supporting their children, with 32% not expecting to get the money back.
Ms Fairbairn said: "As a society, we must make sure that any interventions geared towards helping young adults take their first independent steps in life do not take for granted both the support and sacrifices of their parents.
"For while every 'full nester' hopes that their 'never fledged' offspring will eventually spread their wings and fly, they might find that on their departure they are faced not only with a bare and empty nest, but also radically diminished nest egg with which to secure their financial future."