A lifelong railway fanatic died on a Gatwick Express train after his head hit a signal gantry near Balham, but it is "not possible" to know how it ended up out of the window, a coroner has ruled.

Simon Brown, 24, from East Grinstead in Sussex, was travelling on the 5.05pm service from Gatwick Airport to London Victoria, moving at around 61mph, when the accident happened on August 7 last year.

During an inquest into his death at Westminster Coroner's Court on Wednesday, Dr Shirley Radcliffe recorded a narrative conclusion and said he died of a head injury, with "no doubt" that his head ended up out of the window.

Dr Radcliffe said: "It is not possible with the lack of CCTV to know how he came to have his head out of the window, and whether he did it voluntarily or involuntarily."

She said a fellow passenger on the service heard a "loud thud" and discovered Mr Brown collapsed in a corridor with a "non-survivable head injury", and that he was declared "life extinct" at Wandsworth Common station at 6.47pm.

Dr Radcliffe said the guard's window was open in the area he was found and extended her "deepest condolences" to Mr Brown's family and friends.

She added: "As we have heard he was a lifelong railway enthusiast and a kind, loving, generous young man - much loved by family and friends."

"He was extremely knowledgeable about railways."

During the inquest, statements from Mr Brown's parents were read out to the court by Dr Radcliffe.

They described him as a "handsome, funny and charming" man who enthused others with his passion for railways.

His mother, Jane Street, said there was nothing her son did not know about trains and railways, adding: "He was a railway man through and through. He was neither reckless nor ignorant of the dangers of that environment."

She said he first volunteered on the Bluebell Railway as a nine-year-old and recently took up a position as an engineering technician with Hitachi Rail Europe in Bristol.

His father, Mike Brown, said the week before the accident he had never seen his son so "relaxed, happy and enthusiastic about his future".

MORE: Rail Accident Investigation report finds failures after Simon Brown died from head injuries on train in Balham

The inquest heard evidence from Mark Young of the Rail Accident Investigation Branch and its recently published report into the accident.

It established the distance between the section of the window where Mr Brown's head was positioned and the signal gantry - believed to have been installed in 1952 - was found to be 26cm while the train was static.

Although the clearance complied with standards for existing structures, the inquest heard it was less than an industry-recommended minimum for new structures, where there are trains with opening windows.

Mr Young also noted that a yellow sticker on the door warning people not to lean out of the window when the train was moving existed in a "rather cluttered environment" among many other signs.

In support of this point, Dr Radcliffe said there "could have been a bigger, better notice", adding: "Whether that is enough, we do not know."

The coroner also welcomed the recommendations in the report which call for Network Rail - in collaboration with train operators - to introduce a process for sharing data regarding clearances between structures and trains at window height, so operators can make "more informed decisions" about the management of risk associated with opening windows.

And that train operators, especially with drop windows, should look at the risk posed to passengers and implement measures to mitigate those.

The inquest also heard how carriages with passenger-openable windows no longer operate on the Govia Thameslink Railway network, and an investigation by the Office of Rail and Road into the incident and any potential health and safety breaches, is still ongoing.