The deal is due to be completed in July and brings a return of 3.6 times CBPE’s total investment of £25 million.

The private equity firm backed the management buy-out of Stewart Group from its founder in 2006, led by managing director John Notman-Watt.

Since then, the group has demonstrated strong growth organically and through a series of acquisitions, according to a statement from CBPE.

Stewart Group, which provides inspection, analysis and consulting services to businesses in the minerals sector, has made five acquisitions, including the purchase of G&T Metallurgical Services.

Iain Slater, partner at CBPE, comments, ‘This is a great outcome for us and for Stewart Group. We backed a business plan comprising operational improvement, organic growth, plus complementary acquisitions and it is pleasing to report success in each of those areas.’

The disposal of the group to laboratory testing services business ALS Group is CBPE’s second investment in the testing/inspection/certification (TIC) sector following its previous backing of Moody International.

‘The underlying dynamics of regulation and quality, coupled with the opportunity to invest in internationally diversified businesses, make the TIC sector an area of strong continuing focus for CBPE,’ says investment director Andy Nelson.

The management team, led by Notman-Watt, will remain with the company under its new ownership.

CBPE invests in UK companies with an enterprise value of up to £200 million across a range of sectors.