Raw sewage has been spilling out onto a busy station platform for several weeks, causing a serious heath hazard.

The problem reached its peak in souring temperatures last Friday, when train users at Streatham station had to step over a stream of sewage rising out of a manhole cover in the middle of platform one.

But commuters first noticed the problem a fortnight ago, and despite raising the alarm with station staff, nothing was done until this Monday.

Station owners Southern claim this is because they did not realise the extent of the problem.

"It was absolutely disgusting," said Kath Shawcross, who travels from the station five days a week. "You could see lumps that looked like faeces and bits of toilet paper.

"I had to take a second look because I couldn't believe what I was seeing."

"It is an unbelievable health risk, especially with the high temperatures we have had recently," she added.

She said she had to warn a young child walking straight towards it not to go any closer.

Although people on the platform were able to give each other warning not to go near the affected area, unsuspecting passengers exiting the trains nearby had jump to avoid the vile liquid.

Jonathon Watts, who travels from the opposite platform, said he had noticed a bad smell at the station for a while.

"It has been smelly," he said. "Now I guess I know what it was. It's unbelievable that it went on for so long without anyone doing anything about it."

Liberal Democrat Councillor for Streatham Wells ward Julian Heather has called for the council to serve public health notices on Southern for its failure to diffuse the problem quickly.

A Southern Inspection team visited the site on Monday after receiving a number of complaints from the public and a call from this newspaper.

A spokesperson for Southern said they cordoned off the area but the problem was more serious than they anticipated and another maintenance team would return later.

He said the source of the problem was not yet known.