An elderly British couple whose son was killed in a car crash have mounted a legal battle in a bid to have a grandchild using sperm taken from him and frozen. Natasha and Barry Smith, both 60, are fighting to keep alive the memory of their only child, Lance, who died in November last year aged 36. The couple say they will take the sperm abroad and pay an egg donor and a surrogate mother if they are denied the right to proceed with their plan in Britain. Although he was fit and healthy, Lance wrote a letter six months before his death saying that if he died he wanted sperm taken from him so his then girlfriend could have a child. The sperm was removed 24 hours after he was killed in a head-on collision with a lorry and stored at a hospital in Birmingham, which specialises in fertility treatment. But complications arose when his girlfriend of 10 years decided she did not want to be the mother of his child. Posthumous conception is unusual in Britain but last year at least six children were born years after the death of the father. In all these cases written consent had been given by the father and their wives gave birth to the children. The official Human Fertilisation and Embryology Authority has said the couple's proposal might be accepted if the High Court rules in their favour, but the ultimate decision will be left to the hospital. Tim Hegley from Issue, an infertility support network, was critical of the proposal. 'Infertility treatment should be used to treat infertile couples and help them become parents. It should not be used for social engineering, which is what this is,' he said. Others have said the couple are too old to care for a young child.