Jeremy Corbyn has said a Labour government would “immediately purchase 8,000 properties across the country” to house homeless people.

Interviewed on the BBC’s Marr Show, he said local authorities should be allowed to take over homes that have deliberately been left vacant.

Could the policy work, and do Mr Corbyn’s numbers add up?

Who are the homes for?

In the interview, Mr Corbyn said the 8,000 houses would be for “people that are currently homeless”.

“Homelessness” is a broad term which could include people who have a roof over their heads but are living in unsuitable accommodation or places where they do not have the right to stay. People actually living on the streets are usually classed as “rough sleepers”.

A subsequent press release from the Labour Party clarified they would be for “rough sleepers” with a “history of sleeping on the streets”.

It added: “The new homes would be a mix of ‘move-on’ housing for people leaving homelessness hostels and ‘housing first’… where rough sleepers with complex needs are moved into permanent accommodation quickly to give them a fresh start.”

How many rough sleepers are there?

Monitoring the levels of homelessness and rough sleeping is extremely difficult – and the statistics are unreliable.

In England, figures suggest there are at least 4,750 rough sleepers at any one time. On the face of it, this seems to be at odds with Labour’s plans: if they buy 8,000 homes and give one to every rough sleeper, surely they’d have more than 3,000 homes left over?

However, many experts and organisations believe the official figures for rough sleepers underestimate the scale of the problem. And, in 2015, the UK Statistics Authority ruled that “Rough Sleeping statistics do not currently meet the standard to be National Statistics”.

They are collected by local authorities – but less than 17 per cent of them conducted a proper street count last year.

Instead, the vast majority rely simply on an estimate based on consultations with local agencies. Most estimates are validated by the Homeless Link charity, but the government admits the figures are “subject to some uncertainty”.

So, to try and get better figures, the homeless charity Crisis commissioned its own research, based on data from a wide range of different sources.

It found there were around 8,000 rough sleepers in England in 2016, and another 34,000 living in hostels.

And the figures are rising – predicted to reach 10,000 rough sleepers in England by 2021, and 11,000 in the UK as a whole. (Housing is a devolved matter, so Labour’s policy would likely only apply to England).

Are 8,000 homes available?

We know there are thousands of empty properties: research published earlier this month showed that about 11,000 homes across the UK have been left vacant for at least ten years. These include many privately owned homes.

In his interview, Jeremy Corbyn said the government should reconsider social priorities when “luxury, glossy, shimmering block[s]” of flats are built in areas with lots of rough sleeping.

But FactCheck understands that Labour’s plan to buy 8,000 new homes would not include any private property. Instead, the buildings will come exclusively from housing association stock.

We asked Labour how many housing association houses were currently vacant, but they couldn’t provide a figure. We will update this blog if they do.

‘Immediate’ purchase?

Jeremy Corbyn said a Labour government would “immediately purchase 8,000 properties”.

However, FactCheck has learned that Labour’s actual policy would not see a direct and immediate purchase of 8,000 properties. Instead, it would immediately strike a deal with housing associations.

Then, as they become vacant, properties would be earmarked for people with a history of rough sleeping to move into.

The amount of time houses need to be vacant for, before being taken, would be negotiated with housing associations. Under the plans, housing associations would remain responsible for maintaining the properties.

So how much would all this cost?

Labour could not provide us with a figure. But we understand these would not be regarded as direct purchases by the Labour Party, because it is part of their wider house-building programme.

The money would come out of its capital spend put forward at the last election.

Would the policy make a difference?

An official House of Commons Library briefing says the “most important” reason for increased homelessness is “the continuing shortfall in levels of new house building relative to levels of household formation.”

But when we drill down to look more specifically at rough sleepers, the mix of causes is perhaps a little more complicated.

A recent Parliamentary report identified “reductions in entitlement to Housing Benefit/ Local Housing Allowance” as one of the key factors contributing to the increase in rough sleepers.

But surveys have also shown that relationship breakdown is the single largest trigger of rough sleeping (although the trigger may be different from the reason someone continues to sleep rough over a longer period).

Studies have shown that between 30-50 per cent of rough sleepers suffer from mental health problems and around half have serious alcohol problems, but it is difficult to determine whether this is a cause of continued rough sleeping – or the result of it.

This question has been put to the test by the Housing First scheme which runs in many European countries. It provides rough sleepers with long-term accommodation, without requiring them to address their wider support needs.

Based on this, experts have argued there is now “consistent compelling evidence internationally” to show that providing accommodation is an “extremely effective intervention with people with long-term experiences of homelessness and complex needs, particularly substance misuse issues and/or mental health problems”.

Indeed, the UK government has said that the scheme “appears to have had a positive impact in Finland”.

Of course, there will always be exceptions to the rule. But there appears to be a strong case to support Labour’s idea to provide rough sleepers with long-term accommodation.

Where Labour’s policy is less compelling, however, is in the numbers. Where exactly are these houses? When will they become vacant? And how much will it all cost?