More than 200 people including MPs, churchmen, and relatives filed past her open satin-lined coffin during the service at a north London Pentecostal Church.
Mrs Gardner's son Graham, five, sat only feet from the coffin with his elder sister, Lisa, and his grandmother, Myrna Simpson. He saw police use a body belt and an adhesive gag on his mother at their home in Hornsey, north London, when she resisted attempts to put her on an aircraft to Jamaica. She died four days later.
During a eulogy Lottie Destin, Mrs Gardner's aunt, renewed the family calls for an independent inquiry into her death.
She said Joy had followed her mother to London from Jamaica but had lost her citizenship when her marriage broke down. She said that Joy was born a British citizen but was killed in the name of the law.
Three Scotland Yard officers - two male constables and a woman detective sergeant - have been suspended since the incident. An investigation has been delayed until after Christmas by a dispute among pathologists as to whether the gag caused Mrs Gardner's death. Three series of tests are believed to have been carried out on the body but the final report has yet to be submitted. The delays have led to fierce criticism of the Police Complaints Authority and the police.
Bernie Grant, the Tottenham MP, said Mrs Gardner's death had opened deportation up to debate. He told the congregation: 'Joy was cut down in the prime of her life, cut down by the forces of so-called law and order . . . cut down by a society which once welcomed us to its shores when it needed our labour to do its dirty work, cut down by a country which dragged our ancestors out of Africa in chains and now seeks to send us home in chains when it no longer needs us.'
Samuel Parris, of the Jamaican High Commission, said that the Government felt very strongly about the incident and offered support to Mrs Gardner's family.
The Rev Selwyn Arnold, the Church's National Bishop, said many mourners must be wondering what price 'in dignity, self-worth and pounds and pence' they had paid for UK citizenship.