BRUSSELS - Britain cannot stay a member of the EU nuclear regulator Euratom after Brexit, whether it wants to or not, European Parliament Brexit pointman Guy Verhofstadt said Wednesday. But Euratom could continue its functions with regard to Britain if London signs an association agreement with the European Union following its departure from the bloc, he added.

Membership of Euratom has become a major front between proponents of a “hard” and “soft” Brexit in Britain, after doctors said leaving it could jeopardise cancer treatments. “In my opinion, since in the Lisbon Treaty Euratom and the EU are fully interlinked, you cannot be fully part of Euratom and not part of the European Union,” Verhofstadt told MEPs.

“Because oversight of Euratom is part of the European Union, part of budget and so on,” said the former Belgian prime minister, who was appointed the EU parliament’s Brexit representative last year.

British Prime Minister Theresa May has said she plans to push ahead with plans to withdraw from Euratom, which oversees nuclear activity within the 28-member bloc.

Some Conservative MPs have reportedly warned they will rebel over the concerns expressed by medics about radiotherapy treatments for cancer patients. Verhofstadt said that as part of the “association agreement” that the European Parliament recommended Britain sign with the EU after Brexit, “there can be a request by the UK for Euratom to continue to do the task they can do now.”

“What is not possible is to go out of the union but stay a full member of Euratom.” The Euratom issue will be discussed for the first time during the latest round of Brexit talks between the EU and Britain starting next week, EU negotiator Michel Barnier said on Wednesday.