TECHCITYINSIDER100: We Are Pop Up is now Europe's fastest-growing network of short-term commercial spaces, especially shops. Its peer-to-peer platform brings together pop-up space seekers with landlords. It also helps those with spare space in existing shops to rent them out short term. After starting in the UK, the company has expanded to Europe and now has wider global designs. Co-founder and chief executive Nick Russell explains the platform and the vision to Julian Blake.