The communities secretary has written to Southern rail after video footage emerged of employees pouring water on a homeless man.

The film, which was taken by a member of the public and posted on Facebook, shows a member of Southern rail staff pouring a bucket of soapy water on the floor next to a man outside Sutton station, in an apparent attempt to get him to move.

James Brokenshire, the communities secretary, said: “This shocking act shows a complete lack of empathy towards someone who is vulnerable and in need of help. I am writing to Southern rail to ensure this distressing incident is dealt with swiftly and effectively.”

Angie Doll, the passenger services director for Southern Railway, said the company was taking the incident very seriously and had launched a investigation.

“We suspended the two members of staff seen in the video and a third colleague who we identified from station CCTV,” she said. “We would like to apologise to the homeless man and we are trying to make contact with him to offer help and support.”

Jon Sparkes, chief executive of the homeless charity Crisis, said it was shocking to see homeless people treated inhumanely. “Those forced to sleep on our streets face incredible dangers every day including extreme weather, abuse and as we’ve seen in the news today, early deaths as well,” he said.

“We understand that service providers have a duty to maintain their premises and ensure their customers can use them safely but to face such treatment – especially at the hands of staff members of what should be a trusted public service – is disgraceful. We are therefore glad to hear Southern rail investigating the incident.”

Crisis research shows that a fifth of homeless people have experienced “wetting down” – where an area is covered in water to force people to move on – while living on the streets.

“In modern-day Britain, we cannot condone treating people this way,” said Sparkes. “Those experiencing any kind of homelessness should be supported, rather than degraded and isolated.”