Teenagers are more likely to own a smartphone than live with their fathers, according to a study.

It predicted that almost half of the children sitting their GCSE exams in 2020 will come from a broken home.

In a startling portrait of ‘broken Britain’, the Centre for Social Justice warned that a culture of ‘disposable dads’ had developed in poorer parts of the UK.

Dr Samantha Callan, David Cameron’s former family policy adviser, who co-wrote the report, said that young people should be encouraged to aspire to have children in wedlock.

Referring to a popular hit single, she added: ‘As Beyonce Knowles says in her song, “If you liked it, then you should have put a ring on it”.

’The CSJ, an independent think-tank founded by Work and Pensions Secretary Iain Duncan Smith, warned that the Government was ‘sleepwalking into a family breakdown crisis’.

It claimed broken families were costing the taxpayer nearly £50billion a year, through welfare payments for single mothers and the additional strain on the criminal justice system, because the children of lone parents are more likely to end up in court and jail.

The report said fathers who did not live with their children should be given financial incentives to return to the family home.

They should also have the legal right to be named on their child’s birth certificate, it added. Currently, an unmarried father cannot register his name unless the mother of his child agrees.

Dr Callan called for the Prime Minister to ‘back marriage with money’ and double the transferable tax allowance for married couples to £2,000.

The think tank Beyonce's pro-marriage message from her hit Single Ladies: 'If you liked it, the you should have put a ring on it'

As Beyoncé Knowles says in her song, "If you liked it, then you should have put a ring on it" Dr Samantha Callan

Criticising Mr Cameron, she said: ‘Despite his genuine resolve, when it comes to the most pressing family policy priority of improving stability there is very little to show from that rightly ambitious rhetoric.’

The study found that while 62 per cent of 15-year-olds own a smartphone, only 57 per cent live with their fathers.

Tory MP Andrew Selous said: ‘It’s a very alarming and shocking statistic and a call to action to put strengthening family stability much higher up the political agenda.’

The report warned that the number of single-parent families had risen by 20,000 a year between 2010 and 2013.

It said 48 per cent of children aged five and under in the poorest 20 per cent of families were now from broken homes. The CSJ also found more than 1million children had lost contact with their grandparents as a result of separation or divorce.

The CSJ was set up by Work and Pensions Secretary Iain Duncan Smith, who has argued marriage helps to prevent family breakdown

Christian Guy, the CSJ’s director, told The Sunday Times: ‘For too long family breakdown has gone unchallenged despite the devastating impact it has on adults, children and communities.’ Fiona Weir, chief executive of Gingerbread, the charity that supports single parents, said: ‘Most single parents are doing a good job.

‘Government spending should be focused on policies that make a real difference for families of all shapes and sizes.’

The CSJ predicted that by next year there will be 2million single-parent families.

It found that in the poorest neighbourhoods in the UK, three-quarters of families have a lone parent.

The Government will introduce a marriage tax allowance from next year, in an attempt to recognise the importance of the institution. It means that where one person in a marriage does not use their full income tax allowance, currently set at £10,000, they could transfer up to £1,000 to their partner, helping to reduce their tax bill by as much as £200 a year.