Revenue: £39.9m (+35%)
Net profit: 0%
This audiovisual integrator sneaks into the top 100 on the back of a whopping 35 per cent revenue jump in its year to 31 December 2017, although its net profit thinned from £236,000 to £20,000. Robert Simpson, who founded Electrosonic in 1964, was awarded an MBE last year. The Dartford-based firm, whose clients include Kennedy Space Centre and Eversheds, appointed a new CEO this July in the form of former HCL bigwig John Hancock.