Whether eleven thousand homeless households in Scotland is a huge number or not might depend on how many you expected there to have been in the first place; but also, if you're of a mind to try and personally do something about it, how difficult you think it will be to deal with the problem. For Josh Littlejohn, the entrepreneur who founded socially-conscious Edinburgh café Social Bite, he saw a mountain, yet one which wasn't insurmountable.

Littlejohn is, after all, the man who brought George Clooney and Leonardo DiCaprio to Edinburgh for much-publicised charitable appearances, and who set out to ask for 800 crowdfunded Christmas dinners for homeless people in 2014 and ended up with 35,000 after the campaign grabbed the nation's attention. Now, inspired by last winter's much smaller Social Bite CEO Sleepout in Charlotte Square to raise funds for his planned homeless village in Granton, Social Bite's Sleep in the Park is intended to open up the experience of rough sleeping for charity to 9000 members of the public.

As the name suggests, the evening will begin with a music festival in Princes Street Gardens featuring low-key acoustic sets from Liam Gallagher, Deacon Blue, Amy Macdonald and Frightened Rabbit, a bedtime story from John Cleese, hosting duties by Rob Brydon, and an appearance by Bob Geldof. A minimum charity pledge of £1000 (self-funded or through sponsorship) is required for access. 'Nine thousand people will translate to around £4m, right?' asks Littlejohn. 'We can do a hell of a lot of good with that for starters.'

The money will mainly be spent in partnership with local authorities getting homeless people out of shelters and into mainstream housing. But cash is only part of the story. 'If we have 9000 people sleeping out in the cold under Edinburgh Castle, imagine how much media attention that will gather?' says Littlejohn. 'It's a chance to have the volume of attention on the issue of homelessness amplified to a never-before-seen level, and I think with that we can have a lot of influence in getting this issue prioritised. We need to do something pretty radical.'

Littlejohn skirts the subject of where his passion for tackling this subject originally comes from, but he does tell us how it's been magnified greatly by his work with Social Bite, through meeting more and more homeless people and realising that not only can it afflict anyone, but the odds are stacked against them once they're in that position. His conviction that he can affect change is infectious, and it's possible to see how he can convince even the globally famous to follow his lead (and why Geldof is involved; every bit as much as Live Aid, Sleep in the Park is a gimmick used to grab imaginations as quickly and effectively as possible).

'I love the fact that Josh believes he can change homelessness in Scotland,' says Ricky Ross of Deacon Blue. 'His vision and imagination are an inspiration. We want to be part of the sleepover - for some people this is the norm, so it's good for us to experience what it means to be without a place to stay.'

Amy Macdonald says she didn't take much convincing, and that the fact one of her friends volunteers at the café in Edinburgh made the decision even easier. 'I'll be performing a stripped-down set with a few of my bandmates,' she says. 'We'll keep it as upbeat as possible and hopefully get people dancing, anything to ward off the December chill. I haven't thought through whether I'll be sleeping over yet, but if so I expect it'll be extremely difficult. It's heartbreaking that so many people have to sleep out every single night.'

Littlejohn says it's 'easier to book ex-presidents and Hollywood movie stars' than it has been to pin down most musicians, although in Liam Gallagher – who said 'yes' right away – he has one of the biggest artists of the year in the UK, outside of Ed Sheeran and Rag 'n' Bone Man. 'I think there must be a higher power involved in making these things happen,' he says, noting that artist participation can snowball when agents see acts of significant size involved with a successful event. 'If it works this year we may well make it an annual thing, certainly for a few years, to try and keep building on the momentum.'

Less exciting, but with far more scope for long-term impact, the Scottish Government and various corporate partners are getting involved with Sleep in the Park and listening to what Littlejohn has to say on the subject of homelessness. Which is a good thing, and about time, frankly. 'I can't believe in 2017 that this is still a problem,' says Macdonald, summing up what many, many others believe. 'The idea of Sleep in the Park is great for raising awareness, because it makes homelessness real for so many people. Most of us have been lucky to never have to think about where we'll find shelter, so having an event like this brings it into the consciousness of so many people. Everybody should have somewhere safe to sleep at night.'

Sleep in the Park, Princes Street Gardens, Edinburgh, Sat 9 Dec.