The Duke of Cambridge has spoken out against the scourge of the drug Spice after hearing about its devastating effect on the capital’s homeless.

William and Kate were left moved by the problems the illegal synthetic high is causing rough sleepers – and usage is increasing according to homeless charity The Passage.

The couple toured a central London centre run by the organisation, which has seen an increase in its clients trying the drug at least once.

During the visit the duke told Mick Clarke, chief executive of The Passage: “The fact it was a legal high and that young people were allowed to take it and it leads to addiction is just terrible.”

The synthetic drug is seen as a growing problem, and the biggest challenge the homeless charity faces is that it is cheap, readily available and can exacerbate existing problems like poor mental health.

The Passage carried out a survey of its homeless clients and found 50% had tried the drug at least once in 2016 – when this study was repeated this year the figure had increased to 70%.

Duchess of Cambridge
The Duchess of Cambridge met volunteers at The Passage (Yui Mok/PA)

After giving the couple a private briefing on Spice Mr Clarke said: “There was real empathy that came from both the duke and duchess, they very much care about the issue and I think it marks the way they care about the poorest in society and they take their responsibility to raise those issues, to give it the profile that’s needed, very seriously.

“I think they genuinely get it in terms of the stuff they’ve done around, say, Heads Together (mental health campaign) and I think they really appreciated hearing first hand the terrible effects of Spice.

“How cheap it is to just get, how readily available it is, I think they were shocked and I think it really brought home this is a drug that targets the poorest of the poor.

Royal visit to Evelina Children’s Hospital and The Passage
Kate took part in an arts and crafts session (Yui Mok/PA)

“If you’re on the streets it doesn’t get much worse but if you’re on the streets and then you’re taking something that literally one puff could hospitalise you, in some cases lead to your death or make you out to be a zombie stereotype figure.

“There was a lot of talk around how we break the cycle of addiction, mental health and homelessness.”

Spice, a former legal high, is a form of synthetic cannabis that was banned in May 2016.

During the visit the couple also took part in a Christmas arts and craft session, with Kate helping to make bead bracelets.

She said: “Charlotte would love making these.”

William was asked to help make a Welcome To Xmas Dinner sign, and given an E to cut out.

Kate laughed and raised an eyebrow as William said: “My son knows I’m useless at this, Catherine is the artsy one.”