Unable to find work after the economic downturn, the men huddle together against the freezing cold under bridges across Ealing and Hounslow.
A lack of sanitation and washing facilities has created squalid living conditions attracting rats, drug dealers and disease.
They are known locally as “fauji” which literally translated means “foot soldier”, but in this context it refers to hard-working immigrants without an identity.
The men arrived in Britain illegally to work as labourers when the economy was thriving and there was demand for home renovations and house-building.
Many risked their lives paying criminal gangs thousands of pounds to smuggle them into the country in the back of trucks – a journey which can take several months.
Because they were required to cross borders illegally, the men destroyed their own passports so they could not be deported to India if they were caught.
Now many of them want to go home. But because they cannot prove their identity to the Indian authorities, the fauji are trapped in Britain.
Only the goodwill of Southall’s Gudwara and local volunteers prevents the men starving, or freezing to death.
Randeep Lall, 39, runs the Sikh Welfare Awareness Team, a voluntary organisation that donates food and blankets to the fauji every night.
He told Sky News: “It’s diabolical, disgusting and disgraceful. I can’t believe in this day and age people can live like this. An animal wouldn’t live the way some of these people are.
“Five years ago it wasn’t this bad. Guys were making a good life for themselves and sending money to their families in India who were building massive mansions there.
“Everyone wants to do the same. They think the streets of London are paved with gold. But when they get here they find they’re not.
“The economic downturn has played a massive part in this. These guys depended on people doing extensions and home renovations. Now there is no building work.
“Suddenly we’re dealing with 150-plus homeless in Southall. I know one man living under a bridge who earns £60 a week, if he’s lucky. He sends that money to India to make his family happy rather than rent himself a room.
“If his family knew he was living like this they would be shocked and embarrassed. These men have a lot of pride and would be seen as failures if they returned to India.
“For those that do want to return, the Indian High Commission is making it difficult. If you don’t have an Indian passport, they won’t have you back.
“The Border Agency comes down and finger-prints everybody, then they come back in two weeks and just do the same thing again.
“It shows the Government are doing something, but they’re not doing a lot. People are still living like animals.”
There have also been outbreaks of tuberculosis and many men have begun to suffer mental health problems. Some have turned to heroin as a means of escape.
Under a bridge over the Grand Union canal we found a pile of sleeping bags and blankets.
It was home to two Sikhs who had been sleeping rough for several months. When Sky News arrived, the men appeared to be preparing to inject heroin but the Sky News team were asked to wait while they prayed.
Later they said they had paid an agent £10,000 to smuggle them into Britain and that the average wage for labouring work was just £40 per day.
They blamed low wages on the increasing numbers of migrants who enter Britain legally on student visas who then disappear into the black economy to work illegally.
Both claimed their families were unaware they were living on the streets. Both said they wanted to return to India but were unable to do so without passports.