The new joint venture to be known as NAAA – Nuclear Atkins Assystem Alliance – will be based in France making it more Franco-British than Anglo-French, although both partners hold a 50% stake.

Together the engineering giants have identified a marketplace of more than 200 reactors over the next 20 years in as many as 30 countries.

China is set to be the dominant nuclear building market during this period.

Despite bold global ambitions both partners have agreed to continue to serve their home market as a separate business in forthcoming years of big domestic growth.

The two companies first formed a strong relationship working together on the ITER international nuclear fusion research project in the south of France, after being selected last April as part of the Engage consortium to act as Building Architect Engineer.

Assystems has built up a formidable record with power companies AREVA and EDF, building the new generation of nuclear power stations.

Together the joint ventures claims it can draw on a pool of some 3000 trained nuclear engineers, many trained at dedicated in-house centres.

Keith Clarke, chief executive of Atkins, said: “Nuclear engineering is a key part of Atkins’ strategy going forward.

“The alliance with Assystem will give us a strong platform from which to deliver nuclear services to emerging international markets.

“The combination of our collective nuclear expertise will position us superbly to pursue opportunities in a broader array of markets with a wider range of services which go beyond our considerable presence in our own home markets.”

Dominique Louis, chairman of the Assystem management board, added: “By combining our capabilities and the experience acquired in the French and British nuclear programmes, which are among the world’s most advanced, Assystem and Atkins will together deliver unrivalled nuclear engineering excellence to governments and utilities.”