The Office for National Statistics (ONS) released figures last monthwhich showed that each woman in England and Wales gave birth on averageto 1.91 children in 2007. This compared with a low of 1.63 in 2001, anda peak of 2.93 children per woman in 1964.
Ms Margo said that the highest increase since 1973, when women gavebirth to an average of two children, could be attributed to a range ofmeasures to support families, including improved maternity and paternityleave, Sure Start and the introduction of tax credits.
She said that in the past the decision whether or not to have childrenand how many to have was often determined by the availability of supportfor families.
'Now there is lots of support in terms of tax credits, so people areable to take the decision to have children knowing that they will besupported with things like childcare,' she said.
'We are not able to see from the figures what kind of people are havingmore children. There are indications that it includes more middle-incomefamilies, which would suggest that they are finding it easier to balancehaving children with working.'
Another key factor in the rising birthrate may be migration from easternEurope and what Ms Margo termed countries with 'higher fertility'.
She said the rate could be being pushed up 'superficially' by people whomay not stay in the country permanently and whose children may notbecome part of the labour market.
The increased birthrate, which has coincided with continued strong salesfigures for the retailer Mothercare, has also been reflected inScotland, where for the first time in a decade births outnumbereddeaths, with a net gain of 1,100.
Jonathan Sher, director of research, policy and practice development atChildren in Scotland, said that one year's rise or fall in thepopulation and birthrate 'does not make a trend'.
But he added that if the Early Years Framework being developed by theScottish Government and the Convention of Scottish Local Authoritiesproduces the promised 'transformational' change for the better, it couldencourage people to have babies and raise families in Scotland.