The letter also asks the STRB to find ways of using the pay system to deal with the teacher recruitment and retention crisis, particularly in London and the South-East. It suggests that the next teachers' pay deal should be a "minimum" increase, introducing the possibility for the first time of local pay variation. Last year, the Governmentintroduced "golden handcuffs"-bonuses of up to £15,000 for teachers in areas of staff shortage, if they stayed in the profession for three years. But last month, ministers acknowledged that these had not been widely taken up. In March, the National Union of Teachers closed more than half the schools in London in a one-day strike over pay, the first industrial action over pay for 30 years.