Lynne Lasenby (39) has been told son Shaun Barnes would have died instantly from the injuries he suffered when he and friend Luey Storr were both fatally hit by a train at St Germans, but said she is still tortured by the thought of Shaun lying undiscovered for so long.

The boys, both aged 17, were killed by the 5.56am Lynn to King's Cross, London, train on Saturday, December 8, but their bodies were not discovered until 8.30am when a driver travelling in the other direction spotted them near the line. In a tragic twist of fate, Shaun's mum was on that train, travelling into Lynn to buy Shaun's Christmas presents.

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Mrs Lasenby, of Wensum Close, Watlington, said: "I know what happened is Shaun's fault for going on the track, but it's very hard to think the driver knew he had hit something but no-one bothered to check what."

Mrs Lasenby is also calling for investigations to be carried out into the brightness of train lights, believing if they were stronger Shaun and Luey may have had earlier warning of the oncoming train.

A spokesman for First Capital Connect, operator of the train which hit Shaun and Luey, said the lights on the train conform to industry standards, as did the actions of the driver.

Head of communications Sarah Pinch said: "We take the safety of our customers and staff very seriously indeed and invest heavily, along with our industry colleagues at Network Rail and the British Transport Police, to make people aware of potential dangers.

"It's always terribly sad when there are accidents on the railway, and we extend our sympathies to the friends and families of the two young men killed recently.

"Despite the work undertaken by Network Rail and the British Transport Police, sometimes that advice is ignored, and anyone who walks onto a railway line or close to overhead power lines, is dicing with death."

She added: "I am confident that our drivers acted responsibly in these circumstances. As is accepted industry practice and compliant with industry and company standards, when a driver reports hitting something, the next train through is asked to search the area. This is what happened at this time."

• Treasured photographs of teenager Shaun Barnes, taken in the weeks leading up to his death on the railway line at St Germans, have gone missing.

A film containing the pictures was taken into Tesco, in Downham, to be developed in the week after Shaun's death in December, but has never been seen since.

Mrs Lasenby said the store has done all it can to find the photos, but they have not turned up and she fears another customer may have been given them by accident.

She said: "I'm desperate for them because I haven't got hardly any recent photos of Shaun."