Revenue: £86.7m (+67%)
Net profit margin: -3.4% Staff: 398
This unified comms specialist cracked open a £60m war chest handed to it last year by private equity backer Mayfair when it acquired £13m-revenue Microsoft partner Modality Systems this June. A lack of new accounts means we've had to recycle old numbers covering its year to 31 December 2017, which show a £2.9m net loss on revenues of £86.7m. As well as holding eight Microsoft Gold accreditations, GCI also partners with Enghouse, Cisco and Fortinet.