A seven-year-old boy can have radiotherapy treatment, following surgery on a brain tumour, against his mother's wishes, a High Court judge has ruled.

Sally Roberts, 37, a New Zealander who lives in Brighton, East Sussex, said she feared that radiotherapy would cause long-term harm to her son Neon, and argued that "credible" alternative treatment was available.

Specialists treating Neon accepted that there were side-effects to radiotherapy but said that without the treatment the youngster could die within a few months.

Mr Justice Bodey, who heard evidence at a hearing in the Family Division of the High Court in London, said radiotherapy treatment could start. He said: "The mother has been through a terrible time. This sort of thing is every parent's nightmare. But I am worried that her judgment has gone awry on the question of the seriousness of the threat which Neon faces."

Ms Roberts had told the court she was not a "bonkers mother". She said she feared that radiotherapy would reduce Neon's intelligence quotient (IQ), shorten his life, put him at risk of having strokes and make him infertile. And she told the judge that she wanted medics to consider alternatives.

Neon's father Ben, who lives in London and is separated from Ms Roberts, had agreed to radiotherapy but was "apprehensive", the court heard.

A specialist treating Neon had told the court that a team of experts involved in Neon's care had agreed that radiotherapy treatment was in the boy's best interests. He said doctors wanted to start radiotherapy treatment as soon as possible. And he suggested that Neon could lead a "good life" after receiving radiotherapy treatment.

Lawyers representing doctors involved in Neon's care told the judge that Ms Roberts was proposing "experimental therapies", which were "unproven", as alternatives to radiotherapy.

Mr Justice Bodey had said he had to balance risk against benefit in deciding whether to allow doctors to use radiotherapy treatment. He told lawyers: "It is a balance between the disadvantages of radiotherapy and the improved prospects of living. You can only suffer these detriments to your life if you are alive."

Mr Roberts said he hoped Neon would be allowed to deal with "ongoing medical issues" without further publicity.