London, England - A ban on a teenage girl wearing a "purity ring" was attacked at the high court today as an "unlawful interference" with her right to express her Christian faith.
Lydia Playfoot, 16, is one of a group of Christians at the Millais school in Horsham, West Sussex, who wears the ring as a sign of her belief in abstinence from sex until marriage.
The teenager claims her secondary school, which allows Muslim and Sikh students to wear headscarves and religious bracelets, is breaching her human rights by preventing her from wearing the ring.
But authorities claim the band, which is engraved with a Biblical verse, is not an integral part of the Christian faith and contravenes its uniform policy.
Today, human rights barrister Paul Diamond, appearing for Lydia, argued that secular school authorities had no right to set themselves up as arbiters of faith and "cannot rule on religious truth".
He asked deputy high court judge Michael Supperstone QC to declare that the school had acted outside its powers when it banned the wearing of the purity ring.
He also claimed that the school authorities were violating Lydia's right to "freedom of thought, conscience and religion" under article nine of the European convention on human rights.
It is not the first time students have faced school bans over Christian symbols.
Earlier this year, 13-year-old Catholic schoolgirl Samantha Devine was told not to wear a crucifix on a chain because it breached health and safety rules at the Robert Napier school, in Gillingham, Kent.
The school said the only exception it would make to its uniform rule would be if the jewellery was an essential part of a particular religion, which they did not feel was the case for the teenager.
Today Mr Diamond told the court at the start of a one-day hearing that the case raised a number of issues relating to Lydia's religious beliefs.
He said the question the judge would have to answer was: "What are the religious rights of schoolchildren in the school context?"
Speaking before the hearing on BBC Breakfast this morning, Lydia said: "In the Bible it says you should remain sexually pure and I think this is a way I want to express my faith.
"I think in the society we live in today with lots of pregnancies and STDs, something like this is quite important and should be taken hold of."
Lydia completed her GCSE's last week and has now left the school.
But today, her father Phil Playfoot said they were continuing to pursue the case because his daughter represented many thousands of young people who had made the same commitment.
"I think an important principle is at stake here. I think Christians should be respected for their views and beliefs," he told the BBC.
"As other faiths are allowed to express their views through the wearing of headscarves or the Kara bracelet of a Sikh, I think Lydia should be able to wear a ring as an expression of her faith."
The purity ring is part of a US-based sexual abstinence programme called the Silver Ring Thing.
The bands are inscribed with a reference to the biblical verse I Thess 4:3-4, which translates as: "God wants you to be holy, so you should keep clear of all sexual sin. Then each of you will control your body and live in holiness and honour."
Lydia's parents, Phil and Heather, are part of the volunteer team that runs the UK branch of the Silver Ring Thing, based in Horsham, West Sussex.
Mr Playfoot is the parents programme director while his wife is the company secretary, according to the scheme's website.
The case at London's high court is expected to last all day today although it is not clear when a judgment on the hearing will be given.