Millar will join Spencer next month from Costain where he was Operations Director of the firm’s £397m-turnover Natural Resources division.

Millar replaces founder and current CEO Charlie Spencer who will become Chairman of the company.

Prior to his eight-year stint with Costain, Millar spent 10 years with Amec managing key projects for customers in the UK, Russia and North America.

Millar is also President and a member of the Management Board of the Engineering and Construction Industry Association (ECIA).

Charlie Spencer said: “Frank’s vast experience, particularly in the oil and gas industry, will be extremely useful to Spencer Group going forward.

“Process engineering is a capability we want to build upon within the business and there are very significant construction and engineering opportunities, particularly within the oil and gas sector, that we wish to explore.

“Frank comes to us with exceptional credentials from his work with two highly-respected, Stock Market-quoted engineering groups.

“That experience will be invaluable to take Spencer Group further forward from what is already a sizeable business.

“I am moving up to Chairman because I recognise that the business needs a CEO with Frank’s experience to take it forward.

“As Chairman I will still be actively involved in the business and in its strategic direction, but I will be handing over the day-to-day running of Spencer Group to Frank and a very experienced existing management team and supporting them fully in developing the business.”

Millar said: “I was looking for a new business leadership challenge and Spencer Group clearly offers that. It’s an exciting business with a strong presence and excellent reputation in the markets it currently operates in.

“It has a very clear preference towards innovation and developing new ideas and that’s very attractive, appealing and challenging.

“My ambition for the business it is to lead it into new markets, taking the company’s high-level engineering capability and growing into more sectors than the business is currently represented within.

“The skills that Spencer employs through innovations such as in the dehumidification of suspension bridge cables, the challenging work it does in the rail industry, projects around biomass handling and the way it has found opportunities in waste markets are all evidence of an organisation that is constantly looking for a different solution to a customer’s problem.

“That is appealing and there is a great market for it, not just in the oil and gas industry but also in sectors such as nuclear, which is constantly looking for innovative solutions to the challenge of the UK’s waste legacy.”