Supsersize classes could become the new norm, it is feared, as new figures show that the secondary school population is set to swell to 3.3 million within a decade.The hike is fuelled by a baby boom in the early 2000s, as well as a high birth rate among women from immigrant communities.The bulge in the population of children has been making its way through the school system, passing up from primary to secondaries.Secondary pupil numbers are expected to rise by 14.7 per cent in the next 10 years, meaning there will be another 418,000 children in secondary schools by 2027, according to Department for Education’s (DfE) latest projections.–– ADVERTISEMENT ––The official forecast will spark fresh concern about the increased class sizes, as well as the squeeze on school places. Professor Alan Smithers, director of the centre for education and employment research at Buckingham University said that the “explosion” in the secondary school population means that class sizes will “almost certainly” rise.“It couldn’t have been a surprise [to officials] as they have seen the numbers coming through primary schools,” he said.“So there really ought to be some plans in place. In essence we are inheriting the whirlwind of Labour’s lax immigration policy.” In essence we are inheriting the whirlwind of Labour’s lax immigration policyProfessor Alan Smithers The DfE’s forecast said the increase in school pupil population is “largely driven by an increase in the birth rate rather than direct immigration”.It went on: “However, that birth rate is in turn affected by any increase in the number of children born to non-UK born women (compared to those born to non UK-born women). “The number of children born to non-UK born women increased by around 75 per cent between 2002 and 2013 (the years in which many children currently in schools were born), although this was a period of increased births generally.”Primary schools have seen an increase in pupil numbers in recent years, but this is now levelling off, the forecast said. There is projected to be around 4.5 million primary-age pupils by 2027, down around 112,000 compared to around 4.6 million this year. Prof Smithers added that the squeeze on school places will be felt more acutely in inner city areas than rural communities. “Population isn’t spread evenly throughout the country and people of different ethnic backgrounds tend to cluster with each other,” he said. “Many of the most affected areas will be the inner cities where lots of the new arrivals to the country have settled, with large families that will greatly increase demands on schools in those neighbourhoods.” A report published by the Public Accounts Committee (PAC) earlier this year warned that there is a “growing sense of crisis” in teacher recruitment against a backdrop of soaring pupil numbers.Ministers have failed to “get a grip” on teacher retention, MPs said, adding that it is “particularly worrying” that the number of secondary school teachers has been falling since 2010.The report found that the DfE has a “disparate collection of small-scale interventions” to address the crisis in teacher retention, but these are “inadequate” and fail to address the underlying issues.A Department for Education spokesperson said: “This Government has driven the largest creation in school places in two generations and by 2020, there will be one million more new places across the education system than there were in 2010. Even with a significant rise in pupil numbers in primary schools in recent years, primary class sizes have remained pretty constant.” Secondary pupil numbers are expected to rise by 14.7 per cent in the next 10 years Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.