Duffel's system connects with airlines’ booking channels more extensively than those of incumbent operators, like Amadeus and Sabre, meaning it can facilitate selling not just seats on a plane, but also other products such as speedy boarding, airport transfer and seat selection.

Add-on products make up an increasing part of airline revenues but are mostly sold through airlines' own websites at the moment (whereas bookings are increasingly being made via intermediaries like Skyscanner). Duffel's technology will make it easier for airlines to sell more of these ancillary services, which is what makes its product so attractive to airline customers.

Duffel's main competitor in Europe, Amadeus, has several billions in revenue and over 15,000 employees, so there's a big challenge ahead, but a big prize if the company succeeds in capturing some of that market.