Reserved Occupations
On 27th April 1939, Parliament passed the Military Training Act. This act introduced conscription for men aged 20 and 21 who were now required to undertake six months' military training.
Parliament also passed legislation that protected some occupations from national service. After consulting with business leaders, in November 1938 the government published the Schedule of Reserved Occupations.
On the outbreak of the Second World War, Parliament passed the National Service (Armed Forces) Act, under which all men between 18 and 41 were made liable for conscription. The government also published details of the reserved occupations if they exceeded the stated age. For example, lighhouse-keepers were reserved at eighteen, whereas physicists were reserved at twenty-one.
Employers were also able to ask for individual key workers employed in one of these key occupations not to be conscripted into the armed forces. By the end of 1940 more than 200,000 men had been granted deferment at their employers' request.
Primary Sources
(1) Ethel Robinson lived in Liverpool during the Second World War. She wrote about her war experiences in Jonathan Croall's book, Don't You Know There's A War On (1989)
My husband had wanted to go in the navy, but he had spondylitis in the spine, which is a form of arthritis, so they wouldn't take him in. He was shattered really, because he'd set his heart on getting into the navy. Which they found he had spondylitis, they couldn't give him any treatment, so he had to just pet on with it. He had to give the pub up and go and work on the docks, repairing ships. It was horrible, he'd never done anything like that in his life, you see, and it nearly killed him. He had to climb rigging and climb over ships' sides and things like that. Then, after the children were born, he had to go and work in the Royal Ordnance factory, making guns on shift work, and he hated that as well. But he wouldn't go on the disabled list, not with the sort of jobs they offered you then. So he stuck it out actually.
Although he couldn't go to the war, he'd get a lot of women saying, "Why aren't you fighting for us? My husband's out fighting for you." Well, you just don't bother to answer; and these were the same women who were carrying on with all kinds. This was the abuse they used to get, men that were working during the war, a lot of abuse from women and other men.