Each year, the Department for Eduation and Skills decides how many places to ask the Teacher Training Agency to fill, using a complicated series of formulas. Like the allegorical butterfly that is responsible for a hurricane on the other side of the world, a small miscalculation in one element of the formula can have disastrous results for teacher supply.

During the past few years, vacancy rates for primary teachers in London have been rising rapidly. In January 2002, they were double the levels reached in 1996. Indeed, the 600 unfilled posts this January represented a third of all vacancies for primary teachers in England. These vacancies arise despite a healthy demand for primary postgraduate certificate in education courses, now the most important training route.

Although applications declined, in the two years before the pound;6,000 training grant was introduced in March 2000, they have now reached record levels. By September some 18,000 people applied for the approximately 8,000 places on offer.

Clearly, rising primary school rolls have helped fuel the demand for more teachers. Extra teachers have also been needed for the smaller class sizes at key stage 1. The Chancellor’s extra handouts to schools also increased the number of teaching posts on offer. Since new teachers have normally been able to find a teaching post closer to home, they have often been reluctant to move to London when they finish their training.

It is vital therefore that sufficient training places are available within London to meet the capital’s own needs.

Thus, London’s share of the extra 1,000 PGCE places this autumn, should ensure that several hundred new teachers will be available next summer to work in the capital’s schools.

With the extra demand for nursery places created during the past few years also largely now satisfied, any additional new teachers next summer will help reduce vacancy levels; that is, unless the Government model has underestimated the number of teachers reaching retirement age.

John Howson is a visiting professor at Oxford Brookes University and a direct of Education Data Surveys