A headteacher is urging pupils to be vigilant as police make extensive enquiries into a stranger approaching schoolchildren on separate occasions.

Louise Whitby, head of Giles Junior School in Stevenage’s Durham Road, sent an urgent message to parents on Thursday after reports that pupils had been approached by a man.

She said: “It has been reported to us that a man has been hanging around near the underpass and park after school this week. A small group of our children have been approached by him but acted in a safe manner. A parent has logged a description of a man wearing grey with a grey beanie hat to police so they are aware.

“Please talk to your children about being observant if they are walking alone and encourage them to walk with a friend if possible. If any parents have further information from their children please log this with the police.”

It follows an incident the previous week, on October 8, when an 11-year-old schoolgirl was approached by a stranger in Stevenage’s Stanley Road and offered a lift in his car. When she walked away, the man drove off towards Raleigh Crescent. Police say at no point did the man attempt to grab or touch the girl.

This man is described as about 30 years old, white, about 5ft 11in with a short beard, possibly a moustache, and wearing a hoody.

The car is believed to be a black estate with a registration beginning with V.

Of the latest incident, a Herts police spokesman said: “Police received a report of a 10-year-old schoolgirl being approached by a man in Durham Road at around 3pm on October 15. It was reported the man tried to check if the girl was ok after he thought she might have been teased by other children. He then walked off towards the underpass by The Oval. At no point did the man attempt to grab or touch the girl.

“The man is described as white, aged in his forties and of a slim build. His clothing was grey and he was wearing a hat.

“Extensive enquiries are being carried out and anyone who saw what happened, or has information, should call 101, quoting ISR 476 of 15 October.”

Police say their enquiries include establishing whether or not the incidents are linked.

Anyone with information about the Stanley Road incident, call 101 quoting ISR 507 of October 8.