Britain has told the EU that it retains the right to return radioactive waste back to the bloc if an agreement on nuclear regulation is not reached.

The warning comes as the UK government puts pressure on Brussels to cooperate on the nuclear issue.

“It might just be a reminder that a boatload of plutonium could end up at a harbour in Antwerp unless an arrangement is made,” one nuclear expert told the Financial Times.

Failure to secure a nuclear deal with the EU could disrupt UK supplies of nuclear reactor parts, fuel and medical isotopes vital for the treatment of cancer.

Around 500,000 scans are performed in the UK every year using imported radioisotopes, The Guardian reported.

A paper outlining the government’s negotiating position highlights the UK’s right “to return radioactive waste … to its country of origin” once it leaves the Euratom Treaty should talks with the EU collapse.

The Euratom Treaty, officially the Treaty establishing the European Atomic Energy Community, regulates the nuclear industry across Europe, safeguarding the transport of nuclear materials, disposing of waste, and carrying out research.

The UK joined Euratom when it became part of the European Economic Community (EEC) in 1973.

Almost 20 percent of the UK’s 126-tonne stockpile of radioactive materials originating from EU countries such as Germany, Italy and Sweden.

The waste has been stored at the state-owned Sellafield plant in Cumbria since the 1970s.

The UK Department for Business, Energy and Industrial Strategy said negotiations with Brussels would focus on the “legal ownership not [the] physical location” of nuclear materials.