The married teacher missing with his teenage pupil might not have been identified under a new law that comes into force next week.

Teachers will become the first group of people in British legal history to be given automatic anonymity when they are accused of a criminal offence. The move could hinder searches like the one for missing teacher Jeremy Forrest, who is thought to be in Europe with his 15-year-old student Megan Stammers, said critics.

The provision, in section 13 of the Education Act 2011, gives anonymity for a teacher when the complaint is made by or on behalf of any pupil at the school at which the individual teaches. The anonymity remains in place until the individual is charged, but can be lifted if an application is made to a magistrates' court.

Bob Satchwell, executive editor of the Society of Editors, condemned the implementation of the provisions as an attack on freedom of speech.

"It will be a criminal offence for anyone - pupil, parent, police, school, local authority, whistle-blower, media - even to inform parents or the general public that an identified teacher has admitted that the allegation is true and has resigned, has been disciplined, or even cautioned for the offence," he said.

Parents would even be banned from discussing the allegations with their neighbours or other parents with children at the school, Mr Satchwell said. And the accused teacher could be disciplined, sacked and move on but unless they are charged with a criminal offence, no one could name them and even the new school might not be allowed to know there was a problem, he added.

A Department for Education spokesman said: "This change will not affect cases like the one currently getting national attention. The police, media organisations and others will be able to apply to a magistrate for an order lifting teacher anonymity.

"If it is in the best interest of the child, this will be granted straightaway so the public can help the police. No teacher who has been charged with an offence, or where a warrant for arrest has been issued, will enjoy anonymity. While situations like this are not common, it is the case that malicious and groundless allegations against teachers have been a serious problem in our schools."

Meanwhile, Mr Forrest's father Jim, of south east London, fought back tears as he begged his son or the teenager to call or email home. He said: "Hi Megan, hi Jeremy, I hope this message reaches you and you are both OK. There are a lot of people back home that are desperate to hear from you. All I am asking is for one of you to make a call, send an email, so we know you are both safe."

Sussex Police has said it had received seven phone calls reporting possible sightings of the pair across Europe after Megan's disappearance was featured on the BBC Crimewatch programme. The force would not reveal where the potential sightings had been made, but said investigators were following up the claims.