Britain and America are two countries that, in recent years, have led the world in attempting to give disabled people rights and equality. During his presidency, George Bush Senior was proud to sign the Americans with Disabilities Act while the 1995 Disability Discrimination Act has gradually transformed the lives of disabled people in the UK. It may appear on the surface that the UK and USA have nothing in common with Nazi Germany, a regime that is estimated to have killed 200,000 disabled people and forcibly sterilised twice that number.

However, there is a dark side to the history of the two partners in the "special relationship" that has quietly been forgotten and swept under the carpet. It is a history that is deeply uncomfortable, disturbing and shameful and which seems to contradict the values America and Britain claim to uphold. This makes it even more vital that light is shone upon this history. Even if it is painful to do so, the past must be confronted and acknowledged.

This story begins 150 years ago. In 1859 Charles Darwin published his groundbreaking book Origin of Species which expounded his theory of evolution by natural selection. It wasn't long before scientists and political theorists began to apply Darwin's theory to human beings. With the spread of ideas about "the survival of the fittest", social Darwinists started to question the wisdom of providing care to the "weak" on the grounds this would enable people to live and reproduce who were not meant to survive. They feared that offering medical treatment and social services to disabled people would undermine the natural struggle for existence and lead to the degeneration of the human race.

Such views took hold not only in Germany but also particularly strongly in America and Britain. The existence of disabled people was increasingly seen in the UK and USA as a threat to social progress. Darwin himself wrote in his 1871 treatise, The Descent of Man, "We civilised men.... do our utmost to check the process of elimination; we build asylums for the imbecile, the maimed and the sick.. .Thus the weak members of society propagate their kind."

It was a British man, not a German, who first came up with the term eugenics in 1883. Francis Galton was a cousin of Charles Darwin and he became obsessed with Origin of Species, especially its chapter on the breeding of domestic animals. This inspired him to spend much of his life studying the variations in human ability. He wrote: "The question was then forced upon me. Could not the race of men be similarly improved? Could not the undesirables be got rid of and the desirables multiplied?".

Galton was convinced a person's mental and physical abilities, like the plant and animal traits described by Darwin, were essentially inherited from one's parents. He grew concerned that eminent British people were marrying late and having too few children. Galton wrote in his 1869 book Hereditary Genius: "Let us do what we can to encourage the multiplication of the races best fitted to invent, and conform to, a high and generous civilisation, and not, out of mistaken instinct of giving support to the weak, prevent the incoming of strong and hearty individuals."

Galton argued that early marriage between healthy, mentally strong families should be encouraged by financial incentives, and reproduction by the "feeble-minded" should be curtailed. In his mind, superior mental and physical capabilities were advantageous not only to an individual but essential for the well-being of society as a whole. To try to spread his ideas, he even wrote a novel Kantsaywhere, about a society ruled by a Eugenic College that followed a eugenic religion designed to breed fitter, more intelligent humans. Galton's views were not regarded as eccentric or offensive at the time. Far from it. In fact, he received many awards during his career. He was made a fellow of the Royal Society in 1860 and was knighted shortly before he died.

Galton's writings played a key role in launching the eugenics movement in the UK and America. Supporters of eugenics called for government policies to improve the biological quality of the human race through selective parenthood. They linked physical and learning disabilities to a range of social problems including crime, vagrancy, alcoholism, prostitution and unemployment. Eugenics quickly gained many backers on both sides of the Atlantic, including leading politicians and opinion formers.

It wasn't just figures on the extreme right of politics who backed the eugenics philosophy. Some of British socialism's most celebrated names were among the champions of eugenics - Sidney and Beatrice Webb (the founders of the Fabian Society), Harold Laski, John Maynard Keynes, even the New Statesman and the Manchester Guardian. They hoped that a eugenic approach could build up the strong section of the population and gradually remove the weak. In July 1931, the New Statesman asserted: "The legitimate claims of eugenics are not inherently incompatible with the outlook of the collectivist movement. On the contrary, they would be expected to find their most intransigent opponents amongst those who cling to the individualistic views of parenthood and family economics."

Many early left-wing thinkers wanted government to direct social policy towards "improving" the human race by discouraging reproduction among those sections of society deemed to have undesirable genes. Supporters of state planning often found the idea of a planned genetic future attractive. As Adrian Wooldridge, author of Measuring the Mind: Education and Psychology in England 1860-1990, comments: "The Webbs supported eugenic planning just as fervently as town planning." Beatrice Webb declared eugenics to be "the most important question of all" while her husband remarked that "no eugenicist can be a laissez-faire individualist".

Similarly, George Bernard Shaw wrote: "The only fundamental and possible socialism is the socialisation of the selective breeding of man." Bertrand Russell proposed that the state should issue colour-coded "procreation tickets" to prevent the gene pool of the elite being diluted by inferior human beings. Those who decided to have children with holders of a different-coloured ticket would be punished with a heavy fine. HG Wells praised eugenics as the first step towards the elimination of "detrimental types and characteristics" and the "fostering of desirable types" instead.

None other than William Beveridge, the architect of the post-1945 welfare state, was highly active in the eugenics movement and said that "those men who through general defects are unable to fill such a whole place in industry are to be recognized as unemployable. They must become the acknowledged dependents of the State... but with complete and permanent loss of all citizen rights - including not only the franchise but civil freedom and fatherhood". A belief in eugenics was certainly not confined to the jackbooted far right.

As the end of the 19th century approached, eugenicists were becoming increasingly influential in British politics. A Royal Commission on the Blind, Deaf and Dumb concluded in 1889 that intermarriage between these groups was to be strongly discouraged. Its report was based upon advice from Alexander Graham Bell, the inventor of the telephone, who had warned in his 1883 work Memoir upon the Formation of a Deaf Variety of the Human Race that the "passions of the deaf and dumb are undoubtedly strong". In 1896 a pressure group entitled the National Association for the Care and Control of the Feeble Minded was set up in Britain to bring about the lifetime segregation of disabled people. Its campaigning reached its peak in the run-up to the 1910 general election.

Advocates of eugenics made significant advances during the Edwardian period. In 1907, the Eugenics Education Society was founded in Britain to campaign for sterilisation and marriage restrictions for the weak to prevent the degeneration of Britain's population. A year later, Sir James Crichton-Brown, giving evidence before the 1908 Royal Commission on the Care and Control of the Feeble-Minded, recommended the compulsory sterilisation of those with learning disabilities and mental illness, describing them as "our social rubbish" which should be "swept up and garnered and utilised as far as possible". He went on to complain, "We pay much attention to the breeding of our horses, our cattle, our dogs and poultry, even our flowers and vegetables; surely it's not too much to ask that a little care be bestowed upon the breeding and rearing of our race". Crichton-Brown was in distinguished company. In a memo to the prime minister in 1910, Winston Churchill cautioned, "The multiplication of the feeble-minded is a very terrible danger to the race".

In 2012, athletes from around the world will assemble in London for the Paralympic Games, a global event which celebrates the talents and achievements of disabled people. However, a century earlier, in 1912, London was the setting for an international gathering with a very different and more sinister agenda - the first International Eugenics Conference. Organised by the British Eugenics Education Society and dedicated to Galton who had died the year before, 400 delegates attended including illustrious figures such as Winston Churchill (who was then First Lord of the Admiralty), Lord Balfour and a number of European ambassadors.

Charles Darwin's son, Major Leonard Darwin, presided at the conference. In the run up to the First World War, he lobbied the British government to establish flying squads of scientists, with the power of arrest, who would travel around the country identifying the "unfit". Those classified as such would be segregated in special colonies or sterilised.

The eugenics campaign continued to gain momentum in the interwar years. Membership of the British Eugenics Society reached its peak during the 1930s. The 1934 report of the Departmental Committee on Sterilisation chaired by Lord Brock recommended legislation to ensure the 'voluntary' sterilisation of 'mentally defective women'.

Supporters of eugenics in Parliament included the Labour MP Will Crooks who described disabled people as "like human vermin" who "crawl about doing absolutely nothing, except polluting and corrupting everything they touch". A bill for the compulsory sterilisation of certain categories of "mental patient" was proposed in Parliament in 1931 by Labour MP Archibald Church. He claimed it was necessary to stop the reproduction of those "who are in every way a burden to their parents, a misery to themselves and in my opinion a menace to the social life of the community". Although such legislation was never actually passed in Britain, this did not prevent many sterilisations being carried out under various forms of coercion.

Eugenics still received backing in eminent circles in Britain until well into the 1940s. Leading economist John Maynard Keynes served on the governing council of the Eugenics Society and was its director from 1937 to 1944. Even in 1946, Keynes was calling eugenics "the most important and significant branch of sociology". On the evening that the House of Commons debated the Beveridge Report, Beveridge himself spoke at a meeting of eugenicists at the Mansion House.

While a belief in eugenics is now largely a thing of the past, the values underpinning it have not gone away. Only 25 years ago, a British MP was prepared to publicly voice the view that a disabled child was an unnecessary drain on society's resources. During a House of Commons debate on abortion in 1985, an MP asserted that to abort a "handicapped" foetus could save the country £1 million over the course of a lifetime.

In my next column, I will explore how America embraced the eugenics cause with even more keenness than Britain and the horrifying impact this had on disabled Americans.