Research from parental rights group Pregnant Then Screwed showed 80% of fathers are offered just two weeks of paternity leave by their employer, with 28% unable to use all their allotted time.
A further 10% took no leave at all because they couldn't afford not to work.
A quarter (25%) continued to work while on paternity leave, with 50% saying that their employer expected them to do so.
This left the majority (80%) of fathers saying they didn't have enough time to bond with their child.
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Employers offer up to 52 weeks maternity leave for new mothers.
The statutory weekly rate of paternity pay in the UK is £156.66, or 90% of average weekly earnings (whichever is lower). Mothers get the same pay, in addition to 90% of pre-tax average weekly earnings for the first six weeks.
Joeli Brearley, founder of Pregnant Then Screwed, said: “The UK’s parental leave policies are the least generous in Europe. Paternity leave has huge benefits for families and the economy. It improves the wellbeing and educational attainment of children, it improves the mental and physical health of mothers, and it ensures a more egalitarian split of the unpaid labour.
"The UK is falling way behind other Western nations when it comes to parental leave, but the government seems happy to ignore this issue despite the obvious benefits to families and the economy."
In addition to improved finances and better parent/child bonding, extending paternity leave would help improve working parents' wellbeing.
The research showed 45% of dads experienced a new mental health issue within the first two years of their child's life, with 70% suggesting that longer parental leave would have had a positive impact on their mental wellbeing.
Overall, 97% of working fathers felt two weeks was insufficient time for paternity leave, and 99% said that the government should improve its offering.
Brearley added: "For too long fathers and same sex parents have been denied a fair amount of paid parental leave. This adds to inequality both at home and at work. It’s time to change things up. That’s why we’re calling on the government to offer all new parents a minimum of six weeks paid leave at 90% of their salary when they become a new parent."
Pregnant Then Screwed surveyed 7,461 fathers between May and June 2022.