Police released shocking CCTV today showing a man with a toddler punching a pregnant woman in the face at a train station.
Officers said the hooded attacker turned on the woman after bumping into her with his pushchair in a busy passageway at London Bridge station.
He punched the 39-year-old woman, who was six months pregnant, after she asked him whether he would apologise for running into her.
Pc Clive Thomas, who is responsible for the inquiry, said the woman went to hospital where both she and her unborn baby were given the all clear.
He said: "This was a particularly nasty and violent attack on a pregnant woman, particularly as the CCTV footage shows her holding her stomach prior to the attack.
"She was taken to Guys Hospital following the assault and both she and her unborn child were checked out by maternity staff.
"Fortunately the woman's baby was unharmed, although the mother was left very shaken and distressed by what took place."
The attack took place on Friday September 17, at about 12.40pm, as the woman, from south Croydon, walked down a sloped walkway to a platform.
Witnesses said the man struck the woman on the right side of her face, leaving it bruised, after she asked if he would apologise for bumping in to her.
He can be seen on the CCTV holding a snack in his mouth before pushing his face close to the woman who is backed against a wall.
Another passer-by can be seen remonstrating with him as the confrontation escalates and the man lashes out while holding his buggy with the other hand.
Investigators found the attacker boarded the 12.42pm service to Brighton, on platform five, with the toddler and a woman with blonde hair.
They have begun examining CCTV from stations along the route to see if they can find where they got off.
Pc Thomas added: "This attack took place in broad daylight at a time when the station was very busy with passengers. I urge anyone who saw what happened, or who recognises the man pictured in the CCTV footage to come forward and contact us."
:: Anyone with information should call British Transport Police on 0800 40 50 40 or Crimestoppers, anonymously, on 0800 555 111.