The "baby gap" between the number of children Britons want and the number they actually have is over 90,000 a year, according to new research by the Institute for Public Policy Research (IPPR) published this week.
The report calculated that if women in their 40s had been able to have as many children as they say they want in their 20s, there would be an extra 13% more children born in Britain each year.
The report recommends introducing pay for the current unpaid 13 weeks parental leave, including a "daddy month" - at least 4 weeks specifically allocated to fathers on a "use it or lose it" basis.
The report also suggested increasing paternity leave pay from £106 per week to 90% of average earnings and extending the period of paid leave from 2 to 4 weeks.
“Fertility patterns can take up to 40 years to change so politicians need to start taking action now”, said Nick Pearce, IPPR's Director.
The average woman forgoes £564,000 in earnings over her lifetime if she has her first child at 24 compared to a similarly educated childless woman; but if she waits until 28, she will forego £165,000.