In Scotland's current music landscape, FLY Open Air is a major success – a twice-annual outdoor club event with a huge audience, a first-rate roster of DJs and a growing international presence. Although it still happens every autumn at its original home in the heart of the city at Princes Street Gardens, it's the event at Hopetoun House in May which gathers the most attention; a weekend party at a scenic stately home just outside Edinburgh, in the shadow of the Forth Bridges.

This month, guests including Nina Kraviz, Peggy Gou, Sven Vath, Solomun, Seth Troxler, Éclair Fifi and Honey Dijon will gather, while the success of the event has inspired individual indoor dates at major Edinburgh concert venues like the Usher Hall and Leith Theatre. With plans for a fully-fledged camping festival in summer 2020, FLY's founder and promoter Tom Ketley tells us how it all started and where it's going.

'I came to uni in Edinburgh ten years ago, and when I got here I ran club nights to pay me through,' Ketley tells us (he's originally from Bridge of Weir, just outside Glasgow). 'I started off outside (infamous student nightclub) Cav, handing out wristbands for 50p, and rose through the ranks from there! Off the back of that I started my own club night, then ended up with my own venue in my last year of uni, when I was 21. That failed massively, because we were spending so much on these big international DJs who would sprinkle a bit of magic for two hours, but when the name wasn't there neither was anyone else.'

The venue was Castle Clvb in the West End of the city, whose brief year in existence many might remember. Ketley decided to keep going, but in a much smaller way, so he starter FLY as a Friday-nighter with a local guest focus at Cabaret Voltaire on Blair Street; at the same time, he was training to be a stockbroker in the day job. 'To be honest, I hated it,' he recalls. 'I had no interest in it. I thought, I can't do this for the next thirty years, just staring at a screen typing in numbers.'

This was 2013, and FLY was a hit from the start with a revolving repertoire of established and upcoming local guests, and in tandem with FLY's success, a number of them – Denis Sulta, Theo Kottis, Jasper James – have gone on to widespread acclaim. 'We were filling the club by midnight, and there was a queue up the road,' says Ketley. 'That's what led us to do the festival - I thought, we really need to do somewhere bigger, and I knew the Ross Bandstand (in Princes Street Gardens) never gets used for anything, even though it can hold two thousand folk. I knew we could fill it if the council would let us.'

Convincing Edinburgh Council to let him try was a year-long process, as 'it's right in the heart of the city and there would essentially be a pounding techno rave going on while loads of tourists are wondering what on earth's happening. But I found the council to be really supportive, mainly because when I phoned up to book they said, 'what day do you want it? It's never booked by anyone, so have whenever you want.' Ketley quit the stockbroker job and put every penny and more into 2016's first FLY Open Air. 'We were skin of the teeth that it worked,' he recalls. 'I opened five bank accounts, five overdrafts, got three credit cards … I ended up going for a drink with the managers of all the artists that had played, and I got a round in and my card got declined. Literally every penny I had to my name was on the line.'

The event was enough of a success that he decided to do another the following spring, however. The site was booked, tickets were put on sale, and close to 2000 were sold – only for the council to tell him that the site was double-booked with a Christian march. The frantic search for a new venue turned up Hopetoun House, which worked perfectly. 'In many ways it was so much easier to do it there, because it was owned by one person, Lord Hopetoun, so there wasn't as much toing and froing with different departments. Looking at the site afterwards, we realised it had potential to grow with more stages and more days.'

The first FLY Open Air at Hopetoun House came in May 2017. Since then both locations have returned once a year and the Hopetoun one has grown, with the Usher Hall and Leith Theatre being pressed into use last Christmas. 'The main thing about our business is, we want to do good music for good people in great locations,' says Ketley. 'We've always tried to do cool stuff, even before this kicked off we were renting warehouses in the Cowgate – real Del Boy and Rodney stuff, just trying to jimmy it together. A lot of the time it was a total shambles, but we learned a lot from them.

'It's now something I'm addicted to, finding venues,' he continues. 'Sometimes I'll see somewhere when I'm out driving, and stop and ask if I can rent the place for a few hours. it makes it more special when you can go somewhere that's not just a big shed, that's got more character. I'm going to launch a camping festival next summer, I can't say where it is, but it's just outside Edinburgh and I think it'll be our best venue yet, it's got everything. The goal was always to do a camping event – I feel like a festival isn't really a festival unless you're camping, and now T in the Park is dead, Rock Ness is dead, Wickerman too, Electric Fields is no longer camping … if we're selling 8,000 people per day for two days, I feel those people would much prefer to camp.'

The question of facing off Glasgow and Edinburgh's music scenes is an old and tired one, but it really has felt in the closing years of this decade that the balance in terms of club events has shifted; that the success of FLY plus Terminal V's huge events at Ingliston has made Edinburgh a clubber's destination once more. Ketley is strongly inclined to agree.

'When I started, Edinburgh definitely wasn't as big as it is now,' he says. 'Maybe I wasn't looking hard enough, but Glasgow was traditionally where it was at; it was more of an industrial city and more people live there. You've got Sub Club, though, which is one of the best clubs in the world, but all the DJs just want to play there, and because it's so small it makes it harder for promoters to do other stuff. I know Glasgow also has Riverside, but the amount of tickets we're selling in Edinburgh is huge now. This city has become a massive market for clubbing.'

FLY Open Air is at Hopetoun House, near Edinburgh, Sat 18 and Sun 19 May.