Britain has reportedly warned the EU that it could send radioactive waste black to the bloc if Brexit talks turn sour.

UK officials have got tough with their counterparts in Brussels by telling them that nuclear material could be shipped back to Germany, Italy and other EU countries.

Britain has the world's largest stockpile of civilian plutonium at Sellafield nuclear plant, with 126 tonnes of the stuff - and nearly a fifth of this originally comes from overseas.

A nuclear expert who has advised the British government told the Financial Times: 'It might just be a reminder that a boatload of plutonium could end up at a harbour in Antwerp unless an arrangement is made.'

Brexit Secretary David Davis met with EU negotiator Michel Barnier on Monday to kick off the latest round of Brexit talks. The UK has reportedly told Brussels it could radioactive waste back to its shores if the talks on leaving the European Union break down without agreement

Britain has imported used nuclear fuel from Europe since the 1970s and reprocessed it at the Sellafield.

The process produced reusable uranium and plutonium, but also stockpiles of radioactive waste which officials are now threatening to send back unless a deal is struck.

EU diplomats hit back at the threat by telling the paper they would have 'the coastguard ready'.

The warning come as Theresa May has faced a growing threat of revolt from her backbenchers over Britain's relationship with the EU on nuclear issues after Brexit.

She has come under mounting pressure to commit to keeping Britain in Euratom - the European nuclear agency which develops and shares nuclear energy - after we leave the bloc.

But Mrs May has insisted the UK must leave the agency on Brexit because so we can free ourselves from the jurisdiction of the European Court of Justice.

Theresa May, pictured leaving No.10 for PMQs today, has insisted that the UK must leave Euratom - the EU nuclear agency - when we Brexit so we can leave the jurisdiction of EU judges

Meanwhile, a government paper setting out Britain's stance in the Brexit negotiation fired off the same warning stressing that the UK has the right 'to return radioactive waste . . . to its country of origin'.

And it said EU countries have responsibility for some 'special fissile materials' - the most dangerous and tightly-regulated types of nuclear substances - derived from imported spent fuel.

Britain has the world's largest stockpile of civilian plutonium at Sellafield, but a plant built at the site to recycle the plutonium into new nuclear fuel was closed in 2011 because of technological flaws.

The plutonium is currently stored as powder in flasks while under heavy guard.

A new plant would have to be built to either recycle the material or process it so oit can be returned safely as waste.

The UK Department for Business, Energy and Industrial Strategy said negotiations would focus on the 'legal ownership not physical location' of nuclear materials.

What happens to materials once ownership has been settled 'will be a matter for the owner and the UK to agree on commercial terms,' it added.