A source said last night: “The man was an admirer who was over-zealous.

“He found out there were some open lectures at the school and attended them.

“He left Emma alarmed when he approached her and started talking to her about the Potter films.

“The school was informed and so were Emma’s parents. The decision was made to call in the police as the man was not known to her.

“A minder was also hired to be with her.

“The police spoke to the man and he was warned off in no uncertain terms. There have been further incidents since they spoke to him.”

A pal of Emma’s said: “Not only was this worrying for Emma but also very frustrating.

“She and all the other young actors on Harry Potter have made great efforts to lead normal lives.”

“They have schooled as normally as possible around the acting roles, have lots of school friends and hobbies and are just young people growing up.

“Considering how they could have let fame affect them they are all incredibly grounded, none so more than Emma.”

The friend added: “She will try not to let this change the way she has to live her day to day life, but obviously the priority is her safety.”