In the south of France, the largest scientific experiment mankind has ever embarked upon is rising out of the ground. This facility, the Iter project, will demonstrate nuclear fusion power on a commercial scale, involving the European Union, US, Japan, South Korea, China, Russia and India. Fusion is the process that powers the sun and the stars, and bringing it to Earth has long been a staple of science fiction fantasies.

It is an energy source that, instead of burning fossil fuels, uses water; it produces no long-lived waste and can operate alongside solar, wind and other renewables to power the world to a carbon-free future. Iter will be operational within a decade and will represent a huge step towards fusion, revolutionising the way we generate electricity in the middle part of this century.

For decades, the UK has led the world in addressing this grand challenge. The fusion (or sticking together) of types of hydrogen to release energy requires the fuel to be heated to temperatures 10 times that of the sun. The harsh conditions required for fusion are a challenge for even the most robust of materials. International partnership has always been crucial to overcome these challenges; the complexity of the science and engineering and the cost of building large test reactors make it difficult for one nation to go it alone.

Currently, my organisation, the UK Atomic Energy Authority (UKAEA), operates the world’s largest fusion experiment, Joint European Torus (Jet), on behalf of Europe. In so doing, we have acquired unique capabilities in critical areas for fusion – robotic maintenance, material testing and fuel handling to name just a few – enabling us to help UK industry to win contracts on Iter totalling more than £450m already (which could rise to more than £1bn).

In the longer term, the UK’s nuclear industry together with UKAEA is well positioned to be a world leader in designing and exporting fusion power stations. However, both the operation of Jet and the UK’s participation in Iter are a result of our membership of the Euratom treaty, an agreement on European nuclear co-operation that dates back to 1957. On 29 March, the UK government declared an intention to leave Euratom at the same time as leaving the European Union.

For decades, the UK has led the world in addressing this grand challenge.

For the UK, a pioneer of fusion research and development since the 1950s, it would be the worst possible time to take a back seat in the race to develop this transformative technology. Currently, we have a contract from the European commission to operate Jet until the end of 2018, employing more than 1,000 highly skilled scientists and engineers. It is imperative that we rapidly find a solution for a continued relationship with Euratom.

The UK government has made a number of supportive statements about retaining our excellence in fusion research and development, as well as a firm commitment to continue paying the UK’s fair share of Jet costs beyond 2018. This is very welcome, and offers some reassurance to my staff, which includes some of the brightest minds in the world, but a more comprehensive and complete solution is still required. The existing Euratom R&D programme comes to an end in 18 months and the European commission is already formulating the future programme.

One of the options available is an association agreement with Euratom, a bespoke arrangement where the UK could remain inside Euratom with certain conditions and constraints. Both Switzerland and Ukraine have such associate status having negotiated mutually beneficial, but very different, deals. Whichever route government takes, it is vital that we negotiate a quick and seamless solution for a strong future relationship with Euratom, giving us every chance to preserve and build on the UK’s leading role in this world-changing technology.

Professor Ian Chapman is CEO of the UK Atomic Energy Authority