A third of working fathers use their paid annual leave so they can afford to take time off after the birth of their children, a new study has revealed.
New fathers are entitled to two weeks' paternity leave at the statutory rate of £138 a week, with just one in six employers topping it up, according to parenting website Mumsnet.
A survey of more than 1,000 mothers found that four out of five couples wanted the father to take more paternity leave, but most men could not afford it.
Only 13% of workers describe their employers as family friendly, while two-thirds did not.
Justine Roberts, chief executive of Mumsnet, said: "It's good to see the importance of fathers in babies' lives being recognised but in practice, we're not yet getting basic paternity leave right. It ought to enable dads to spend time with their new babies, but because of the woefully low rate at which it's paid, they're forced to take annual leave or miss out altogether.
"The companies we work with through our Family Friendly programme reap real rewards by supporting employees in their family lives. It would be great if this became the norm, not the exception."
Deputy Prime Minister Nick Clegg said: "It's quite unfortunate that so many parents are unable to take time away from work to care for and support their young children, and it is bizarre that even in the 21st century, hundreds and thousands of hard-working parents are having to abide by Edwardian rules when it comes to juggling their work and family lives.
"We need a modern Britain that works for modern families, not against them. I've fought hard in Government to bring about that change, whether it's through the introduction of flexible working, free childcare, shared parental leave or equalising paternity pay, so that men can spend more time with their newborn child without being penalised financially.
"The tide is certainly turning but as this Mumsnet survey shows, we need to go much further. So, I'm calling on employers to set an example when it comes to offering flexible working arrangements so that working parents are empowered to make their own decisions in their own time."
Mumsnet will tonight give awards to family-friendly companies, including Butlins, Matalan, McDonald's and Unilever.
Deloitte, PwC and Shell, who between them employ nearly 100,000 people in the UK, have announced that they will be offering enhanced paternity packages to all their employees.
Gaenor Bagley, executive board member and head of people at PwC, said: "We have always offered flexible working to all and will now offer fathers the same benefits we offer to mothers through our enhanced maternity package. I see this as being a critical move to level the playing field, and an integral part of PwC's strategy, to ensure that all of our employees have the same options and opportunities."
Emma Coddenham of Deloitte UK, said: "We have made the support for our working parents a firm-wide priority and we're pleased to see the Deputy Prime Minister's call to action, encouraging other businesses do the same. The potential positive impact of the changes that the Government is introducing is significant for working families across the UK.
"Our plan to introduce enhanced shared parental leave is just one part of a much bigger picture of practical support that we provide to our people to ensure that they are able to find the right career/life balance. What is clear to us, however, is that any practical support must be accompanied by a cultural shift, and we have worked hard to ensure that the ability to successfully balance career and life is an accepted part of the way we work."
Mr Clegg added: "I'm delighted that Deloitte, PwC and Shell are taking positive steps in modernising the workplace by providing flexible working arrangements for hardworking parents."