Britain is facing a ?baby gap? of more than 90,000 births per year as middle-class professional women delay motherhood to build a career, a report said on Sunday.

As a result, many women have fewer children than they planned because they postpone starting a family until too late in life, the report by the Institute for Public Policy Research (IPPR) found.

The research highlighted the financial differences between early and late motherhood. A woman forgoes 564,000 pounds 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 lose out on 165,000 pounds. Moreover, almost a third of those who give birth early return to a less well paid job than before they became mothers, the report ?Population Politics?, said.

A fall in fertility could have serious long-term consequences, including higher taxes to pay for public services.?Britain is now at a demographic fork in the road and in danger of taking the wrong direction,? IPPR Director Nick Pearce said in a statement. ?Although our population is rising, a fall in fertility would have serious long-term consequences. ?It would make it harder to earn our way in the world and to pay for valued public services.? Pearce urged the government to create a minister for demography and better childcare to enable families to combine work and family life more easily. ?Fertility patterns can take up to 40 years to change so politicians need to start taking action now.?

The report examined the general household survey of 1982-84, in which 1,108 women in their early twenties predicted they would have 2.25 children. But the average family size for those women, now in their forties, is 2.02, meaning 92,000 predicted babies were never born.

The average age at which women have their first child has risen from 23.7 in 1971 to 27.1 in 2004, according to official statistics. One in five women remains childless compared with one in ten a generation ago.