23. Cloudreach

Revenue: £168.6m (+38%)

Staff: 627

The holding company of this cloud migration specialist registered a 38 per cent revenue uptick in its valedictory fiscal year (ending 31 July 2021) ahead of its sale to IT services giant Atos in January 2022. Atos said the deal would bolster its position as "the multi-cloud powerhouse", highlighting Cloudreach's top-level partnerships with AWS, Microsoft Azure and Google Cloud. Previously backed by Blackstone, Cloudreach employed 600 staff at its offices in London, USA, Canada, the Netherlands, Germany, France, Switzerland and India.