Controversial new legislation designed to safeguard the welfare of children will turn teachers into “state snitches” and damage relations between parents and schools, a campaign group has claimed.

Opponents of the move to ensure that every child in Scotland is assigned a “named person” - often a teacher - gathered in Edinburgh on Monday as they prepared to fight the proposals in a pound;30,000 court action.

The Scottish government has said that named persons would do nothing more than was normally expected in their day-to-day work but would record “routine information” if they had concerns about a child’s well-being.

The No to Named Persons campaign argues that MSPs are acting illegally by appointing “state guardians” through the recent Children and Young People (Scotland) Act.

“Teachers and teaching unions have been sleepwalking into this - they think this is simply rebadging what they are already doing,” said Eileen Prior, executive director of the Scottish Parent Teacher Council. But the bar for when teachers would be expected to intervene in a child’s life had been lowered, she insisted.

“The trust between parents and teachers is in danger of being undermined - parents will be very much less likely to ask for advice or open up about something that’s going on in their family life if they think that’s going to be shared far and wide,” Ms Prior added.

Anne Cannon, a mother of five who comes from a family of teachers, said: “I can’t believe that the teaching profession in Scotland has been so silent on this issue. The power in that relationship will now change and I will be very reluctant to say anything to [teachers].”

Alison Preuss, spokeswoman for Schoolhouse, Scotland’s national home-schooling support charity, said that being a named person would turn education, health and social work professionals into “state snitches”, responsible for gathering private information about families.

Liz Smith, Conservative spokeswoman on young people and a registered teacher, said the legislation was “morally wrong” as it was “extending the role of the state at the expense of parents and their families”.

“As a social worker, I can tell you the state makes a lousy parent,” said Maggie Mellon, an independent social services consultant. She urged the disparate group of activists to focus on their shared concern, insisting that any reference made to parents should include gay parents.

Dr Jenny Cunningham, a community paediatrician in Glasgow who spoke in a personal capacity, said the position of teachers would “no longer be one of trust”.

She added that Scotland’s enthusiasm for “early intervention” - the idea that social problems can be averted by picking up on difficulties in early childhood - was ideological and not supported by evidence. Sir Harry Burns, who recently stepped down as Scotland’s chief medical officer, had “made this pseudoscience of the early years and early intervention entirely respectable” among teachers and other professionals, she argued.

More than 150 people attended the event on Monday. A judicial review is being prepared by the Christian Institute, Christian charity Care and the Family Education Trust, among others.

EIS general secretary Larry Flanagan said that his teaching union agreed with the principle of a named person to provide a single point of contact and improve children’s access to services and support. “However, we are also clear that further development is required on the very clear guidance that will be required for all individuals who will undertake the named-person role,” he added.

A Scottish government spokeswoman said: “Named persons - usually a health visitor or a promoted teacher already known to the family - were first introduced in parts of Scotland following parents’ requests for a single point of contact for advice or help when needed, to avoid having to retell their story to different services. Nothing in the legislation changes parental rights and responsibilities because we know that mothers and fathers are, with a very few exceptions, the best people to raise their children.”

The policy was already operating successfully in parts of Scotland, she said, adding: “The legislation was supported by a large majority of those who responded to the public consultation, backed by a wide range of children’s charities and professionals working daily to support families across the country and endorsed by the Parliament.”

The government advises that named persons can offer help but that parents are under no obligation to accept it.