The proportion of children born to unmarried mothers hit a record 47.5 per cent last year, according to the Office for National Statistics. The figure has risen from 25 per cent in 1988 and just 11 per cent in 1979.
If the trend continues at the current rate, the majority of children will be born to parents who are not married by 2016.
Conservative MPs and experts warned that the stark decline of marriage is likely to lead to more family breakdowns and damage children's prospects.
Tim Loughton, the former Children's minister, called on the government to introduce tax breaks for married couples to help stop the decline. He said: "If people are prepared to make a public declaration to each other in front of their friends and family they are more likely to stay together. Without marriage people drift in and out of relationships very easily.
"In families where parents break up children do less well at school, are more likely to suffer mental health problems and are more likely to have substance abuse problems.

"The government needs to send a very clear message that it supports marriage. That's why married tax breaks are so important."
David Cameron has pledged to introduce legislation to give couples tax breaks worth £150 by the end of the year.
The Prime Minister has been forced to put a timetable on government plans to recognise marriage in the tax system amid growing Conservative unrest over the failure to act.
Last year a total of 346,595 babies were born outside marriage and civil partnerships in England and Wales, equivalent to 47.5 per cent.
In 2002 the proportion was 40.6 per cent, and if the trend continues at the same rate more than half of children will be born out of wedlock by 2016.
According to the 2011 Census, the number of people who are married in England and Wales has fallen from just over half of the population a decade ago to 45 per cent.
The figures represented the first time since the Census was founded in 1801 that married couples have been in a minority.
More than 11 million people in England and Wales are single, reflecting the growing number who have chosen not to marry, while more than 5million unmarried people live with their partners.
A total of 150,000 declared themselves to be in civil partnerships.
The Centre for Social Justice, a think tank founded by the Conservative Work and Pensions Secretary Iain Duncan Smith, has raised repeated concerns about the decline in marriage.
Christian Guy, director of the think tank, said: "Marriage is not a right wing obsession, but a crucial social justice issue. People throughout society want to marry but cultural and financial barriers faced by those in the poorest communities thwart their aspirations.
"Evidence shows quite clearly that children growing up with married parents tend to have better life chances. The Government must deliver on its family friendly pledge."
The official figures show that 729,674 children were born in 2012 and mothers now have an average of two children each, the highest fertility rate since the 1970s.
The rise in the birth rates has been driven by immigration and women chosing to have children later in life.
The number of women aged over 40 having children reached a record 29,994, up from just 6,519 in 2002.
The average age of mothers has risen to 29.8 years in 2012, compared to 27 in 1982. The ONS said: “These trends reflect the increasing numbers of women delaying childbearing to later ages.
“This may be due to a number of factors such as increased participation in higher education, increased female participation in the labour force, the increasing importance of a career, the rising opportunity costs of childbearing, labour market uncertainty, housing factors and instability of partnership.”
The figures also show that one in four new mothers were born outside the UK in 2012, compared to 17.7 per cent a decade earlier.
The ONS said that foreign-born mothers have a higher fertility rate, and are likely to increase their chance of conceiving by having children earlier.
The rising birth rate has been fueled by high levels of immigration from Eastern Europe after accession countries joined the European Union in 2004.
The number of women aged over 40 having children reached a record 29,994, up from just 6,519 in 2002.

Source: Telegraph