Nearly three million people in Britain are in "distressed" relationships where they regularly argue or consider divorce, a new report has found.
The stresses of parenting and financial pressures are heaping strains on relationships, leaving 1.4 million families "at breaking point", the study warned.
Experts said the findings of the Relationship Distress Monitor report are "very concerning" and warned that constant bickering and stresses at home can also have a "far-reaching" impact on children, who on average do worse in school and are more likely to fall into antisocial behaviour and crime.
Dr David Marjoribanks, senior policy officer at the charity Relate which carried out the report, told the Press Association: "It is not just the actual breakdown of the relationship itself, it's specifically the conflict that surrounds that.
"It means that when relationships end it is not deemed to inevitably harm children, far from it. The point is it is the conflict in intact relationships that can be just as damaging, as when relationships end.
"Children who grow up with parents who have highly conflicted relationships are much more likely to have mental and physical health problems, to not do as well at school and end up in antisocial behaviour and criminality even."
Researchers analysed data from the UK household study Understanding Society to shed light on the state of relationships across the UK.
They found that in 2013-14, the most recent year where data was available, 2.87 million people - 18% of married or cohabiting couples - are in distressed relationships.
These are relationships with strains deemed to be "clinically significant" by counsellors.
Parents of under-16s are slightly more likely to be in distressed relationships at 22%, while becoming a parent for the first time "is one of life events most likely to reduce relationship quality", the report found.
Researchers found the number of distressed relationships had fallen from the highs of 2011 and 2012 where 2.5 million couples were in such relationships, but has still not recovered to pre-recession levels.
Dr Marjoribanks said: "There is a pattern of relationship strain increasing during recession years, and that is very much what we would expect.
"Where economic strain increases, for example low income, unemployment, a build up of debt, the strain on the relationship increases.
"But the level of relationship distress hasn't gone back to pre-recession levels, so while we might be out of the woods in terms of recession the impact on relationships clearly doesn't seem to have completely gone."
One in ten partners report at least occasionally regretting getting married or living together, while 9% said they at least occasionally consider divorce or separation, according to the survey of 20,980 people.
Dr Marjoribanks said many couples suffer in silence for years and only seek help when it is too late to salvage their relationship.
He urged the Government to respond to the "concerning data" and "take up the torch lit by this report" and create a national programme to co-ordinate and signpost couples to relationship services.
Relate counsellor Arabella Russell said: "Through my work I see countless couples in distressed relationships. Often the couples I see are arguing constantly with pressures such as jobs, finances and childcare putting their relationships under real strain.
"It's a very painful place to be and the impact it can have on the family is huge."
Relate is launching its first national appeal, Breaking Point, calling for donations to help subsidise vital services to support families whose relationships and finances are under intense pressure.
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