People who turned to their local authority for help were often sent packing without support or instructed to sleep rough in order to access services, according to a report by St Mungo's.
The findings, based on interviews with 40 St Mungo's clients, suggested that three-quarters of homeless people had slept rough the night after they asked a council for help because they had nowhere to stay.
One of those interviewed by St Mungo's said: "We decided to go to the local council and they told us that we had to sleep rough for three nights in a row before they could actually do anything to help us. We just felt complete despair."
The charity is calling on the government to ensure that no one is sent away by local authorities when they have nowhere to go. St Mungo's will take part in a mass lobby of Parliament on Wednesday in support of the Homelessness Reduction Bill.
The research also found that 129 rough sleepers have died in London since 2010, while a quarter reported being physically assaulted when they were on the streets.
One interviewee said: "I've been beaten up quite a few times sleeping in doorways, or even in cars, they smash the window in on top of you, spit on you, urinate on you, try and set you on fire. I've had all of those things happen to me."
In the past five years, the number of people sleeping rough has more than doubled - with a 30% increase in the past year alone.
Howard Sinclair, St Mungo's CEO, said: "It's impossible not to be shocked by what our report has revealed. Too many people are dying on our streets and too many are living with damaging long-term consequences of not having a roof.
"St Mungo's believes that the system for assisting people who are at risk of sleeping rough in England requires fundamental reform.
"The funding package announced by the Prime Minister this week is a promising start. We hope it is the first step to a new and coherent national strategy to end rough sleeping.
"Parliament also has a once in a generation opportunity to improve the current homelessness law. I urge MPs to turn up to support the Homelessness Reduction Bill on October 28 and help persuade the government to back the bill and fully fund the implementation of this new legislation.
"Rough sleeping has doubled since 2010 and continues to rise. Unless further action is taken, more people will experience the dangers of rough sleeping without the support they desperately need."
Mayor Sir Steve Bullock, London Councils' executive member for housing, said: "Councils across London have prevented or relieved nearly 30,000 cases of homelessness in the last financial year.
"Whilst they will strive to continue to help as many people as possible, they cannot do this alone. If we are to tackle what is becoming a growing crisis in our city and across the country, Government must give local authorities the resource and tools to carry out their duties."
A Department for Communities and Local Government spokesman said: "No one should ever have to sleep rough. That is why we have launched a £40 million homelessness prevention programme, including £10 million grant funding for services to help those at imminent risk of sleeping rough.
"We are sympathetic to the aims of the Homelessness Reduction Bill and we are currently considering its contents."