Handbrake turn! U.K. based taxi app Hailo is handing in its private hire vehicle (PHV) license in London and going black cab only, which is where the business began -- only expanding to include PHVs in May 2014 and causing some irate cabbies to attack its offices last year. But from now (5pm U.K. time today) Hailo will only offer the ability to book black cabs in London.