Insurance Act 1920 extended national insurance to 11 million additional workers. This was considered to be a revolutionary measure, in that it extended unemployment insurance to almost the entire labour force, whereas only certain categories of workers had been covered before. As a result of this legislation, roughly three-quarters of the British workforce were now covered by unemployment insurance. The Agriculture Act 1920 provided for farm labourers to receive a minimum wage while the state continued to guarantee the prices of farm produce until 1921. It also provided tenant farmers with greater protection by granting them better security of tenure. In education, teachers' salaries were standardised, and more than doubled from pre-War levels, in 1921 by the Burnham Committee. The Mining Industry Act 1920 placed a mandatory requirement to provide social welfare opportunities to mining communities, while the Public Health (Tuberculosis) Act 1921 increased the obligation of local authorities to treat and prevent TB. Health reforms In 1919, the government set up the Ministry of Health, a development which led to major improvements in public health in the years that followed. Whilst the Unemployed Workers' Dependants (Temporary Provisions) Act 1921 provided payments for the wives and dependent children of unemployed workers. The Employment of Women, Young Persons, and Children Act 1920 prohibited the employment of children below the limit of compulsory school age in railways and transport undertakings, building and engineering construction works, factories, and mines. The legislation also prohibited the employment of children in ships at sea (except in certain circumstances, such as in respect of family members employed on the same vessel). The National Health Insurance Act 1920 increased insurance benefits, and eligibility for pensions was extended to more people. The means limit for pensions was raised by about two-thirds, immigrants and their wives were allowed to receive pensions after living in Britain for ten years, and the imprisonment and "failure to work" disqualifications for receiving pensions were abolished. The Blind Persons Act 1920 reduced the pension age for blind people from 70 to 50. Old age pensions were nearly doubled (from £26 5s to £47 5s a year), efforts were made to help returning soldiers find employment, and the Whitley Councils of employees and employers set up. Cost The reforming efforts of the coalition government were such that, according to the historian Kenneth O. Morgan, its achievements were greater than those of the pre-war Liberal governments. However,