“Why else would I be here if I’m not using this role properly to influence and help people where I can?” says the Prince of Wales about whether he’s the right person to campaign against homelessness.

In a clip from a forthcoming ITV documentary, Prince William describes his work to reduce homelessness through his project Homewards – something critics have questioned as being inconsistent with his privileged life.

He says he comes “with no other agenda than desperately trying to help people who are in need”.

The prince also gave a speech about homelessness this evening in London – where he said: “I passionately believe that it can, and should, be ended.”

Prince William says that for him the point of having such a high-profile public platform is to use it to make a positive impact on problems such as homelessness.

“It’s a big challenge,” he says of his five-year Homewards project, that has built up local and national partnerships to reduce homelessness in six areas around the UK.

“And I like a big challenge, I do like that, but I can’t do it on my own,” he said.

“I think everyone having a right to a safe and stable home benefits us all,” he adds.

Anti-monarchists have accused the prince of being “hypocritical” for his housing project, when he has several homes and has more than £20m from the Duchy of Cornwall as a private income.

But homelessness campaigners such as Mick Clarke, chief executive of the Passage, have welcomed the prince’s involvement – and praises him for using his “considerable platform to say that homelessness is something that simply should not exist in 21st Century Britain”.

“For William this is personal. He has a long history of involvement on this issue, back to when his mother took him to the Passage when he was 11,” Mr Clarke told the BBC.

“As patron of the Passage he has seen first hand, through his many private visits, that homelessness can be prevented and ended.

“That is where the genesis of Homewards came from – through his personal interactions with those experiencing homelessness.”

The prince first went as a child with his mother Diana to the see the Passage’s work in central London – and he has often spoken of this influence on opening his eyes to the world outside of palaces and the challenges facing those without a home.

The prince’s projects have become increasingly direct in their approach and include plans to build social housing on Duchy of Cornwall land.

These will have “wrap-around support” to help settle people who might have complex social, psychological and health needs after many years without secure accommodation.

It’s a “housing first” model that draws on how Finland has cut homelessness, with an emphasis on getting people into housing and then offering intense support.

At an awards event for the Centrepoint youth homelessness charity, Prince William said homelessness was a “complex societal issue” – but repeated once again that it could be tackled.

“Achieving this will require a movement that creates systemic change. A change that focuses on prevention rather than management. And one that ensures all young people have truly affordable options to live and thrive independently,” he said.