Media playback is unsupported on your device Media caption Male sex work: 'Rape has become normalised'

It is estimated there are as many as 100,000 sex workers across the UK, and about 20% of them are male. Some of these men see their work as a positive choice, but for the most vulnerable it can be little more than a means to survive.

It is early afternoon in east London, and Daniel has just finished his first appointment of the day.

After dropping out of university a decade ago, he turned to sex work and has been doing it full time ever since.

"I see mainly single men," he tells the BBC's Victoria Derbyshire programme.

"A large proportion are gay and out, but a lot of the [others] are married and trying to cover up what they're doing."

Image caption Daniel has been doing sex work for about a decade

Daniel says his clients usually fall between the ages of 35 and 85, and his price list includes anything from massages to sexual intercourse and overnight stays - which he advertises through apps and websites.

What he is doing is legal.

In England, Wales and Scotland, sex work is illegal when someone is forced to sell themselves against their will, solicits for work on the street or keeps a brothel.

About 80% of male sex workers now have an online presence.

For Daniel, it is a safer way of offering services - he also refuses to participate in unsafe sex and "chem sex", which involves the use of drugs.

But many others put themselves at risk of harm.

'Child exploitation'

About 5% of male sex workers operate on the street, and Manchester has more male street workers than anywhere else in the UK.

Hayley Speed, who works for The Men's Room, one of only a handful of charities across the UK that supports these men, trying to keep them safe, says: "When we speak to sex workers about when they first got involved in sex work, the phrase we hear most often is, 'I started when I was 14 or 15,'" she says.

"That's not sex work, that's child exploitation."

Image caption Some male street sex workers operate around Canal Street in Manchester

Ms Speed fears that many sex workers - both children and adults - are being abused.

A new survey into internet-based sex work, Beyond the Gaze - given ahead of publication to the Victoria Derbyshire programme - has found over 12% of the male sex workers who responded said they had been sexually assaulted in the past five years.

More than 70% of male respondents in the survey - the biggest of its kind in Europe - also said they were unlikely to report crimes to the police.

Ms Speed says many male sex workers do not take sexual assaults - including rape - seriously.

She believes there has been a "normalisation of quite extreme behaviours", with many simply viewing this as "[par for] the course".

Image caption Fergal McCullough and Hayley Speed's outreach helps some of the most vulnerable sex workers

The hub of Manchester's male street work scene is beneath the city's gay village, around Canal Street, on the canals that line the centre of the city, where The Men's Room does two night's outreach a week.

According to its co-director Fergal McCullough, sex workers in this area are the most vulnerable - some are homeless, nearly all have very little money.

"I wouldn't necessarily say the guys down here have made a rational choice to be in this situation," he says.

"Tyler" - not his real name - began sex work while in a similar situation.

He fled his hometown when his family disowned him for being gay.

With no money, and not knowing anyone in the city, he became homeless. Within a week, he had turned to sex work.

"It started off with one or two people a night, then more and more," he says. "You get to a point where you just shut down."

'Drink spiked'

Such work was both illegal and dangerous.

Sometimes clients who did not want to pay would lock him in their car, he says, and not let him out until he gave them their money back.

He says he was also raped at a hotel, after his drink was spiked.

"When I [arrived], there was one person," he says, "when I woke up, I [was naked] on the bed, sprawled out with four men naked around me... masturbating and everything."

He feared what they would do to him if he tried to leave, but says they were so confident he would not contact police that they just let him walk away.

"They just literally let me leave normally, not even worried about if I was going to say anything - they just literally didn't care," he says.

Image copyright Getty Images Image caption A new survey suggests 70% of male sex workers are unlikely to report crimes to the police

Tyler says many sex workers choose not to contact the authorities as they are "afraid that people are going to be like, 'Well, you're a sex worker, it's your own fault.'

"I think because I'm a guy they [would] think it's not as bad as a woman being raped, but it's exactly the same."

Greater Manchester Police's Det Ch Supt Shaun Donnellan says the force is aware "male rape in particular is under-reported" and encourages any victims to come forward.

"We work tirelessly to get justice for anyone who has suffered and... work closely with [charity] Survivors Manchester to support any men who make a report to us," he adds.

Tyler now has a traditional job and does sex work only occasionally, advertising online.

At the time of his alleged rape, he did not to go to the police.

Watch the Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel.