This firm has benefited from the influx of American firms to Ireland. Working mainly in Dublin, the construction contractor provides clients such as Oracle, Fidelity Investments and Bristol-Myers Squibb with upgrades to their office buildings. It has also moved into new builds. It claims to have 93% repeat business, helping international sales hit £94.7m in 2017. It is led by founder and managing director Paul McKenna, 51, and based in Newry, Northern Ireland.