The amendment would mean that the government could not leave Euratom in March next year unless it could demonstrate suitable arrangements were in place to maintain international standards of safeguarding.
Responding to the government's defeat on Amendment 3, Prospect senior deputy general secretary Sue Ferns said:
“The success of our nuclear industry rests on the world class standards we have maintained as part of Euratom and it is totally right that the House of Lords have recognised that if we have to leave Euratom then we have to have suitable arrangements in place to protect the nuclear industry.
“This government defeat is a recognition that the government needs to do far more to satisfy parliament that they are on track to meet the demanding timetable they have set themselves, simply hoping it will be alright on the night will just not cut it when it comes to nuclear safeguards.
“There is no majority in the House of Commons for undermining nuclear safeguards and now it is up to MPs to stick to their guns and demonstrate that both houses of parliament are united in their commitment to our nuclear industry and the highly skilled people who work in it.”