Insisting both parents were named on the birth certificate would make fathers acknowledge their responsibilities

Unmarried mothers will have to include the name of their child's father on birth certificates under sweeping changes to the law unveiled yesterday.

Men who claim they are being excluded will also get the right to demand a paternity test and be formally acknowledged on registers.

The Government proposals aim to give more children the 'security' of being acknowledged by both parents.

Under its plans GPs or social workers will be asked to corroborate claims that the woman or child would be at risk by naming the father, while those who say they do not know the father's identity would have to persuade the registrar they are telling the truth.

Ministers believe that making it a legal responsibility for fathers to register births jointly with mothers will also make it easier to settle disputes over child maintenance.

Fathers who refuse to be named and mothers who do not record the father's name are liable for a £200 fine.

Work and Pensions Secretary James Purnell, who won a battle against Cabinet colleagues who opposed the plan, outlined the proposals in a White Paper.

Labour's deputy leader Harriet Harman is understood to have expressed concern that the system would tar some children permanently by associating them with undesirable fathers.

But Mr Purnell insisted: 'It's crucial that from the day they are born, both mum and dad recognise the role they play in their child's life and how that shapes their child's identity.

'We want to ensure that while continuing to protect vulnerable women and children, we promote parental responsibility and child welfare by significantly increasing the number of birth registrations which hold the details of both mother and father.'

In 2005 275,000 babies were born outside marriage in Britain. Every year 50,000 have the father's name left blank on their birth certificate.

The white paper would still allow mothers to omit a father's name if they can prove exceptional circumstances  -  including domestic violence or abuse. Children born as a result of rape or sperm donation will also be granted exemption.

Opposition MPs accused the Government of sending out mixed messages on parental responsibility.

Tory work and pensions spokesman Andrew Selous said: 'The Government has completely failed to send a clear message on the need for responsible fathers in children's lives.

'The Government must start making this a political priority by removing the penalties on couples in the tax and benefits system, recognising the contribution of family breakdown to poverty and working practically to strengthen family relationships.'