A radio presenter was threatened with arrest and posters with his face on put up in schools after he tried to investigate pupil safety.
Metro Radio, in Newcastle, decided to test the security of schools in the North East by sending reporter Simon Conway to try to gain access to playgrounds and classrooms.
But they were warned by Northumbria Police that he could face arrest, and soon his face had appeared on posters in schools warning people of his plan.
Metro Radio news editor Justin King said: "Detectives warned us Simon would get arrested if he went ahead with the investigation and they went on to alert local authorities, with some of them sending out their own warnings to headteachers.
"We were told police were following procedure but what was more worrying was effectively a 'wanted poster' of him had appeared at a number of schools in the North East.
"We are still unaware of where the poster originated from.
"Northumbria Police have denied they were the source of it, but someone, somewhere, had thought it would be a good idea to make it.
"He or she used a personal picture from Simon's Facebook page, and distributed it without his permission."
Metro Radio said that if the investigation had revealed robust safety measures at the schools they would have praised them for it.
They also said councils in Newcastle and Gateshead had written to schools asking teachers to remove any posters that might be on display.
Mr Conway said: "We were aware of possible issues, but never intended to cause a nuisance to schools and felt there was a huge public interest argument for our investigation."
A Northumbria Police spokesman said: "The reporter came to us regarding two undercover investigations he was considering.
"We advised him that if he was to break the law during these then he faced being arrested and possible criminal proceedings as would anyone else who breaks the law."