Cuts to mental health services are contributing to an increase in the number of mentally ill people sleeping rough and leaving outreach workers feeling they "can't do anything" for them, campaigners have said.
The number of homeless people in London has more than trebled over five years from 711 in 2009/10 to 2,342 in 2014/15, according to a new report by charity St Mungo's, that provides beds and support to those sleeping rough.
A survey of street outreach workers across England found 62% of them believed the number of mentally unwell homeless people in their area was increasing, which Dan Dumoulin, St Mungo's policy officer, called "pretty strong evidence" that the figure was rising nationally.
He told The Huffington Post UK that cuts to NHS mental health services and supported accommodation for mentally unwell people had limited their options of places to go and made it "a lot harder for them to get off the streets".
"People's mental health problems tend to get more severe as people stay on the streets for longer, it's often the case where people have to deteriorate to the point where they're sectionable or where the police can remove them for their own safety," he said.
"There really is a sense among our outreach staff that it's a group of people for whom they really can't do anything at the moment in terms of actually getting them inside."
He claimed the rise was partly explained by an increase in awareness of mental health issues among street outreach workers who are recording it more but he added: "The increase has been far too large to just be explained by that".
He cited the example of the START service for mentally unwell rough sleepers in South London, which has seen its caseload cut from 200 clients in 2012 to 130 now after the number of staff was halved to cope with budget cuts.
"A lot of people who've got mental health problems, their problems are actually keeping them on the streets, they can't get treatment for those problems, they're going to stay on the streets," Dumoulin said.
"Funding's been cut, which means staffing goes down, which means thresholds for accessing those services increases."
He said: "I spoke to someone in the START service and they told me they'e had to turn people away who are suicidal because they don't have severe enough problems according to the service's threshold criteria... People are being turned away, which means they can't get the treatment they need, which means they're stuck on the streets."
As part of its report, St Mungo's interviewed homelessness professionals across England and 86% said there was not enough specialist mental health supported accommodation in their area.
The charity is calling for more investment in specialist accommodation, saying the lack of beds requires "urgent attention".
Dumoulin referred to the case of a man identified only as Colin whose story reflected the "tragedy that, mental health problems tend to get more severe as people stay on the streets for longer".
Colin lost his job and left his rented home that he could not longer afford and lived on a friend's couch. He began sleeping rough and developed depression and suicidal thoughts. He went to A&E while feeling suicidal but was told to visit a GP.
The man was turned down for housing by his council because he was not a priority need. He moved back in to private accommodation with help from St Mungo's.
St Mungo's is calling on the government to reinvest in mental health services for homeless people, to introduce tougher legal duties on councils to prevent homelessness, a requirement on the NHS to stop people sleeping rough after being discharged from mental health hospitals.
"There's an real urgent need to actually do something for those people," Dumoulin said.
HuffPost UK asked Department of Health for comment on funding cuts had not received a response as this story went live.