The Government is being warned that a "tragedy" will happen if it does not tackle the "appalling" health and safety risks Southern Railway passengers are facing.

Lawyers representing travellers have written to the Department for Transport asking if it carried out any risk analysis in advance of the strikes by the Rail, Maritime and Transport (RMT) union.

The Association of British Commuters said it also wanted to know at what point the DfT will consider risks to be sufficiently serious to warrant termination of the franchise.

The group, which is considering legal action over the Government's handling of the Southern franchise, gave witness reports of incidents across the Southern network during the recent disruption to services.

These included reports of violence at Brighton station, dangerous overcrowding and mass panic in crowds, mass rushes along overcrowded platforms to board trains in the case of last-minute announcements, a child left abandoned on a platform due to overcrowding, and illness and incapacity brought on in the vulnerable, pregnant, elderly and disabled.

Reports have also emerged of at least two incidents of trains going through stations without making planned stops during the course of last week's RMT strike, said the group.

It produced a graphic showing a packed platform, with the message: "It is not a case of if a tragedy might happen but when."

The move came as members of the RMT staged the final day of a three-day strike in the bitter dispute over the role of conductors.

Comments from passengers who contacted the Association of British Commuters included: "London Bridge has been incredibly scary with lots of last-minute cancellations. I'm amazed that there hasn't been a serious accident. On two occasions this week I have been stood on trains on the platform for 30 mins before they have been cancelled. At this time, the trains have been completely full and standing. Once cancelled, there is a race and a huge push to get on the next train to another that leaves within the next two mins."

A commuter from London to Hassocks said: "The level of overcrowding peaks on strike days, but of more concern for me is that there never seem to be any safety-qualified staff either on the stations or on the trains. It is surely a matter of not 'if' but 'when' a serious accident or fatality occurs. Yet only the passengers are the ones who appear concerned by the situation - why is that?"

Another said: "I am now 7 months pregnant and have experienced the worst travel conditions throughout my pregnancy. I am not only having to take a significant detour, but also exposing myself to overcrowding on the trains, which is not only unpleasant but also a health risk for me and my baby. I am regularly getting squeezed and bumped into, and having to protect my stomach from impacts.

"Temperatures due to overcrowding are extreme and I have felt dizzy on several occasions (air con only occasionally turned on and completely ineffective in a crowded carriage). Finding a seat is extremely stressful and although I can claim a priority seat, passengers are so frustrated and angry that I do not feel entitlement to one, which may cause arguments and put me at risk again, unless I have been offered it. I have seen numerous other pregnant passengers experiencing similar issues, as well as young children having to stand up in crowded carriages."

A commuter from Haywards Heath said: "Due to a last-minute cancellation of the overcrowded train we had already boarded, I was involved in a massive rush across platforms - a race for the next train. I was lucky and managed to squeeze on. After some shifting around to get more people on I ended up standing in 1st class. To make more room I and another woman sat on the edge of the tables. Doubtless this is a huge health and safety risk if the train stops suddenly but we took up half the floor space so another person could squeeze in.

"When we arrived at Oxted there was great overcrowding on the platform as people tried to exit - fortunately a member of staff had the sense to open the emergency gates. There are numerous health and safety issues all the way. Soon, someone will fall off the new narrow London Bridge platforms, or down the steep stairs, or passengers will be crushed while on the trains. So many things are bound to go wrong at some stage. We are being utterly exploited because somebody, somewhere will be making a great deal money out of us."

A Southern spokesman said: "We understand our passengers' frustration and have every sympathy for the way they have been subjected to unwarranted disruption by the RMT during this lengthy and futile dispute.

"We deploy additional staff and queuing systems at our busiest stations on strike days to help manage passenger numbers. Generally, on strike days stations tend to be less busy as many people decide not to travel.

"When stations do get busy, such as in times of disruption, our staff's priority is to ensure our passengers can get on and off trains safely, which sometimes necessitates holding passengers back from the platform.

"We once again urge the RMT to put a stop to this strike action for the sake of our passengers."

A DfT spokesman said: "Improving rail services for Southern passengers is a priority for us and the operator. We announced last month that Network Rail would deliver £20 million of improvements and appointed a rail industry expert to lead a project board to drive up performance.

"We have responded to correspondence from lawyers acting on behalf of the Association of British Commuters."

Transport Salaried Staffs Association general secretary Manuel Cortes said: "The Association of British Commuters are not scaremongering. Their report vindicates our union's claims that Southern management are playing Russian roulette with passenger safety and gambling for huge profits with passengers lives.

"Here is yet more evidence that Transport Secretary Chris Grayling is letting the Southern rail crisis run away towards rail catastrophe.

"He must now stop taking advice from the wide-eyed, free-markeering muppets in his department who are driving Southern towards disaster and take Southern back into direct public control to prevent a Southern train crash before it happens."