England needs 47,000 more secondary teachers by 2024 to cope with an explosion in the number of secondary school pupils, Tes can reveal.

The figures - which union leaders described as “eye-watering” and “potentially catastrophic” - mean that the government will have to increase the overall number of secondary teachers by more than a fifth if it wants to avoid rising class sizes.

The news comes at a time when recruitment to teacher training is already down by 19 per cent on last year.

Based on pupil projections from the Department for Education, Tes calculated the extra number of primary and secondary teachers that would be needed to keep the pupil-teacher ratio in these settings in line with the average between 2005 and 2016.

According to the analysis, if the government wants to keep to the average primary school pupil-teacher ratio it has maintained since 2005 (20.1 pupils per teacher), it will have to add nearly 8,000 extra teachers by 2024.

But in secondary schools, where the pupil population is forecast to rise dramatically after a period of decline, many more teachers are needed.

The number of secondary pupils is expected to climb from 3,191,780 in 2016 to 3,838,700 by 2024.

This means that to stay in line with the average pupil-teacher ratio since 2005 (15.1 students per teacher), the number of teachers will have to rocket by 47,000, from 208,100 in 2016 to 254,822 by 2024 - an increase of 22.5 per cent.

The news comes at a time when recruitment to teacher training is already going backwards. According to figures published by Ucas last month, total applications for postgraduate teacher training are down by 19 per cent on the same time last year, and the government has missed its teacher recruitment target for five years in a row.

The extra 47,000 secondary teachers and 8,000 primary teachers that are needed are on top of the numbers needed to replace the teachers leaving the system.

The government says that schools have a record number of teachers. However, figures show that a rise in primary numbers has hidden a decline in secondary teachers.

The Tes analysis also highlights the challenge the government is facing in key subjects. For example, in modern foreign languages, the DfE has a target to recruit 1,500 new teachers in 2018, but only about 6,200 MFL degree-holders graduate with at least a 2:2 each year.

This means 24.2 per cent of all such graduates would have to opt for a career in teaching to meet demand.

Geoff Barton, general secretary of the Association of School and College Leaders, called the figures “eye-watering” and said the government faced a “Herculean” task to find the numbers.

Mary Bousted, joint general secretary of the NEU teaching union, said the figures were “potentially catastrophic”, and doubted that the government would be able to plug the looming gap. “It’s just untenable that you’re going to recruit those numbers,” she told Tes.

A DfE spokesperson said: “There are now a record number of teachers in our schools - 15,500 more than in 2010 - and the number of new teachers entering our classrooms outnumbers those who retire or leave.                                                    

“Earlier this month, the education secretary announced a strategy to drive recruitment and boost retention of teachers - working with teaching unions and professional bodies - to continue to attract the brightest and best graduates.

“This will build on existing recruitment measures, which attracted more than 32,000 trainees last year alone.”

This is an edited article from the 6 April edition of Tes. Subscribers can read the full article here. This week’s Tes magazine is available in all good newsagents. To download the digital edition, Android users can click here and iOS users can click here