A thief walked into school changing rooms while the pupils were at a PE lesson and stole their mobile phones and cash.

It is believed a man was able to walk unchallenged through Rochester Grammar School and got into the changing area while youngsters were busy in the sports hall and playground.

At least 22 mobiles, including expensive iPhones and Blackberry devices, were taken from the Maidstone Road school.

Several girls also had their iPods taken, but it is not clear how much money was stolen.

After the thefts were discovered, all pupils' bags were searched and staff searched the rest of the site, but nothing was found.

Police will be looking at CCTV footage from school in a bid to identify the offender.

One parent, who did not want to be named, said: "The man was able to gain access to the changing rooms and went unchallenged while the girls were doing PE.

"My concerns here are not for the mobile phones which were stolen but for the safety of the pupils who were on the premises at the time."

"i'm pleased to hear security is being stepped up but it's a bit like closing the stable door after the horse has bolted…” – parent

The school has stepped up security measures after the incident last Friday morning and has written to parents to inform them that during school hours certain gates will be locked and additional monitoring of the site will be put in place.

Doors to the changing rooms will be locked during lesson time.

The school is also looking to install sensors on the school gate to alert the school whenever anyone enters the site and install additional CCTV at the entrances and car park.

Head teacher Stuart Gardner said: "From CCTV footage police confirm that this was someone outside the school community. The school has never before had an incident of an unauthorised individual successfully gaining entry to the school buildings."

The parent added: "I'm pleased to hear security is being stepped up but it's a bit like closing the stable door after the horse has bolted."

A Medway Police spokesman said: "Between 9.50am and 10.10am on Friday, it is reported that a man entered the gym area of the school and stole approximately 22 mobile phones, as well as a number of iPods and a small amount of cash.

"No arrests have been made in relation to the incident but an investigation is underway and enquiries are ongoing."

If you saw anything or can help police with their enquiries, phone 01634 792645, quoting reference XY/1354/12 or Crimestoppers, anonymously, on 0800 555111.