Kyle's longing to be a father highlights issues affecting gay men and women - but also the one in six heterosexual couples in Britain who have problems conceiving. They will know first-hand the plight of a young person desperate to be a parent. Baby hunger turns a stroll in the park into a torment because of the mummies and daddies pushing their toddlers on swings. It makes dinner-party conversation about good schools painful, and the school-run traffic bitter as well as frustrating. At its worst, baby hunger sours friendships and destroys marriages.
Medical advances have delivered many of these would-be parents from their misery. Andrew Solomon, award-winning author of Far From the Tree, a book about conventional and unconventional families, tells me how, as a young gay man, he was "riven by my agony at having to choose between my integrity and the urgent wish for children that surpassed almost every other desire for me".
He and his partner, John Habich, had their son George with donor eggs via a surrogate mother, Laura, a friend of Habich's and one half of a lesbian couple whose own two-child family Habich enabled by donating sperm to them.
Solomon, meanwhile, had donated sperm to father a daughter, via in-vitro fertilisation, with his best friend, Blaine, who is bringing the child up with her (male) partner in Texas.
"That I lived through the changes that gave me my family feels nothing short of miraculous," he says. "There are too many unwanted children in Western societies and too few who are longed for, and those children formed not by accident but by deep and careful intent are likely to be among the best-loved in the world."
Solomon sees surrogacy as proof of progress: we have developed into a more just and caring society that helps anyone who longs to be a parent become one.
"I was born to the lie that gay people couldn't have children," he says, "and I am grateful every day that we live in a time when both social mores and medical advances have made it possible for me to have children."
A procedure that allows the conception of much-loved children must be a good thing. Surely it is only humane to use any means possible to help men and women, gay and straight, conceive?
Yes - and yet...
The Cassons' case has ignited huge controversy: the procedure may have taken place in the sterile surroundings of an IVF lab, but the participants' consanguinity raises the spectre of one of the few remaining taboos - incest.
Twitter reaction to the story ranged from "nothing wrong with this" to "gross", "disgusting" and "selfish".
Robert Flello, Labour MP for Stoke-on-Trent South, spoke of his "many concerns and worries" about the case.
Jill Kirby, social policy analyst, finds it "very disturbing that any mother would consider it healthy or appropriate to give birth to her son's child. What is even more worrying is that the High Court has granted the son an adoption order, partly based on the 'closeness' of the relationship between the family members involved."
Mrs Casson countered these attacks by pointing out that Miles, the baby she conceived using Kyle's sperm, "is not biologically tied to me, other than he's my grandson. I love being a parent and for Kyle to experience that. I would do this for him." She and Kyle have said that friends have been overwhelmingly supportive.
Surrogacy cases have increased dramatically over the past few years - in 2012, 167 babies were registered in Britain as born to a surrogate parent.
This marks a huge increase from 2007, when only 47 parental orders were filed to register a baby born through surrogacy, according to figures from the Children and Family Court Advisory and Support Service. The upward trend is continuing: in the first month of last year alone, 24 babies were registered to British parents after a surrogacy. Celebrities from Elton John to Nicole Kidman have turned to surrogacy to have their children, and, in the process, turned the intervention into an acceptable lifestyle choice.
And Mary Portas, the retail consultant whose Secret Shopper programme is broadcast on Channel 4, made headlines recently when Melanie Rickey, her wife, conceived a son from Mary's brother's sperm.
Lawyer Natalie Gamble, whose firm was involved in the Cassons' case, explains that surrogacy using close family members has become commonplace.
"We have seen many instances where sisters, brothers-in-law, cousins, help one another out in this fashion," she says.
"It is difficult to speak of precise numbers, but UK law, which does not permit advertising for a surrogate or for a surrogate to offer her services, is pushing couples to look among family members for surrogacy."
Many childless couples seek help abroad: India, Georgia, Russia, Thailand, the Ukraine and a few states in America allow women to be paid to carry another's child through IVF and embryo transfer.
But international surrogacy raises ethical questions of its own, as shown by the recent case of Gammy, a baby with Down's syndrome born to a Thai surrogate and allegedly left behind by the intended Australian parents.
For Gamble, the only issue raised by the Cassons' case is a legal one. "UK law does not allow singles, like the son [Kyle] in this case, to apply for a parental order, or birth certificate; so the young man had to apply for an adoption order instead," she says.
She is campaigning to change the law, which she says condemns children to forfeit "a UK birth certificate which reflects their true parentage, and instead must either become adopted children, or live in limbo without resolved legal status".
But the Cassons raise more than legal concerns; they raise profound ethical questions too. In a world where anyone can conceive, the family will become a notion so confused that children will struggle to understand the crucial relationships most of us can take for granted. Kinship will become a loose term embracing well-paid strangers and well-meaning relatives.
The Human Fertilisation and Embryology Authority (HFEA) was founded in 1991 as a safeguard against such muddles. Its remit is to ensure that reproductive procedures are ethical and in the best interests of the child. But critics have repeatedly questioned its ability to oversee what goes on in the 77 clinics licensed for fertility treatment in the UK.
The chairman of the authority, Sally Cheshire, is a former accountant who previously headed the Audit and Governance Committee and Licence Committees. The 13 members of her board include lawyers, medical professionals and women who have "relevant personal experience in infertility and unsuccessful treatment". The make-up of the board prompted one lawyer to conclude that "the HFEA focuses on facilitating successful infertility treatments rather than monitoring it".
Beyond the HFEA offices, IVF labs and the tabloid headlines, surrogacy unsettles our notion of family ties - motherhood in particular. Commercial surrogacy raises the prospect of a rent-a-womb industry spreading across the globe, involving young women who seek short-term motherhood for financial gain. Real, lifelong mothering, which engages with children as cherished beings rather than commercial assets, no longer fits in the marketplace of surrogate mummies.
But even when money is not involved, surrogacy raises concerns. Policy-makers, politicians and psychologists agree that the family is the building block of a flourishing society: it provides children with their first experience of identity and security, and their first lessons in right and wrong.
Our traditional notion of "the family" has been stretched to include cohabitation, divorce, step-parents and stepchildren, and gay marriage. Can it stretch further to encompass surrogacy cases where a mother and son have a baby together? Or does this endless manipulation in fact leave the family unit hollowed out, a meaningless husk rather than an inspiring template for all?
Mrs Justice Theis, the judge in the Cassons' surrogacy case, claimed the close relationship between the family members involved had proved a "critical feature".
A report described how baby Miles, now eight months old, "clearly has formulated a secure attachment to the father", adding: "The father understands that the child will need to know about how he was conceived and feels that he will utilise the security of the family structure to support his son in understanding that he is a very much wanted child."
For some, this is enough.
"Hi-tech interventions in reproduction are not necessarily antithetical to the forging of stable, loving relations," says Fergus Greer, a psychologist specialising in the family.
"As long as the child bonds with its primary carer, feels secure and loved, it will do well, no matter how unconventional its conception. If Kyle and Anne-Marie can create this loving home for Miles, he will be able to cope with the revelation of his unusual origins."
The Cassons' case has set a precedent. More and more unconventional conceptions like theirs will ensue, allowing would-be parents to realise their dreams. Solomon welcomes this development, saying: "Why should making children be reserved to two people, and closed to those who, for one reason or another, are not adequately fertile to procreate?"
Kyle Casson agrees: "I did not choose to be gay. I was born that way. I was born unable to have kids. Being a dad was a high priority in my life and now I have done it."
A new life beckons for the Casson family. A new era dawns for the rest of us, too. Infertility, sexual proclivity, marital status: social mores and medical advances have removed every barrier to conceiving.
A new generation, who did not choose to be surrogate babies, will decide at what cost we have satisfied our baby hunger.
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