Revenue: £94.1m (+9%)
Net profit: -33% Staff: 487
This Mayfair-backed unified comms giant's true scale is not reflected in its latest accounts, which show revenue hitting £62.7m in the eight months to 31 December 2018 - a nine per cent pro-rated rise. Having gobbled two sizeable Microsoft partners in 2019 - including Telford-based MSP Nasstar for £79.4m in December - London-based GCI is now comfortably a £100m-revenue business. It holds eight Microsoft Gold accreditations, and also counts Enghouse, Cisco and Fortinet as allies.