Looking back on their first Terminal V event at Edinburgh's Royal Highland Centre in April 2017, promoters Derek Martin and Simon McGrath can admit now that it almost didn't go to plan. 'It only had 2,500 people in attendance, which was half our targeted audience,' says Martin. 'It was a massive risk, rushed massively in hindsight, with many obstacles in our path. We almost moved the event to a smaller location a few days before, but somehow battled through it and things really went onwards and upwards from there.'

'That event was incredibly stressful though; we were starting from scratch as festival promoters, with no support or investors as we're solely independent promoters. We bit off more than we could chew, and we look back at the first event often and laugh at how we actually made it happen. But somehow we did, and now here we are…' The pair can afford to laugh; from an audience of 2,500, Terminal V (it's 'V', not '5') now attracts closer to 15,000.

One-time promoters in their own right with, respectively, the Edinburgh club nights Músika and Xplicit, Martin and McGrath more recently combined forces on the club Nightvision, before consolidating once more as Terminal V. McGrath points out that moving into festivals was always the intention, but the move was forced in 2017 when 'our Nightvision shows really started to outgrow our venues.'

'We're definitely getting a lot of attention nationally now and even on the continent, whereas the first Terminal V was more of an Edinburgh thing,' says Martin, explaining what he believes is the secret of the bi-annual bank holiday party's success. 'We like to think we've stuck to our guns, in terms of our booking, music, production policies, and not compromised quality over easy but bad decisions.' Says McGrath: 'We've always modelled ourselves on the electronic festival experiences you can have abroad, but putting our stamp on it to offer something which we feel is currently uncatered for in Scotland.

Asking the pair to list their highlights is a demonstration of just how many big names Terminal V can attract, with Martin picking out Bicep, Robert Hood and Len Faki in 2018, and McGrath mentioning the Scottish debut of Charlotte du Witte at the first Terminal V, when she was still a relatively unknown act. 'There's lots to be excited about this year,' says Martin. 'Richie Hawtin returning to Edinburgh after eighteen years – which both myself and Simon were on the dancefloor for – is pretty special.

'On the other hand, Patrick Topping went to university in Edinburgh and attended our early club nights, so to have him return as a global star and headline a stage of this size is amazing.' Another Scottish debut will be Phillip Gorbachev ('We were both blown away by his set at Exit Festival in Serbia last year,' says McGrath), as well as old-stagers Mr G, Derrick Carter and Andrew Weatherall.

Alongside FLY's huge events, Terminal V has been at the forefront of a change in clubbing emphasis in Edinburgh over very recent times – as a staging post for large-scale, near-city events. 'When we launched Nightvision in 2014, we were doing over fifty club shows a year,' says McGrath. 'It was launched at a time when there weren't as many acts coming to Edinburgh as other UK cities and our goal was to put the place on the map once again. We're certainly doing fewer club shows, with two Terminal V events per year taking so much of our time, but it's grown to become more national with thousands of people travelling from all over the UK and Ireland to it.'

The mission to raise Edinburgh's clubbing profile looks pretty much accomplished, then. Where do they go from here? 'Growing the festival as much as we can in all respects,' says Martin. 'With our site, we have the luxury of being able to do that, and Halloween 2019 is already shaping up to be even bigger yet again.'

Terminal V: The Rising, Royal Highland Centre, Edinburgh, Sat 20 Apr. Other guests include Helena Hauff, Daniel Avery, Mall Grab, Nastia, Maceo Plex, Objekt and Green Velvet.