Britain's negotiating position in Brexit talks is "as good as it was" before the Conservatives' disastrous General Election result, Theresa May has insisted.

The Prime Minister called the June 8 poll telling voters she needed them to strengthen her hand at the negotiating table in Brussels as the UK withdraws from the European Union.

But Mrs May has now insisted the position has not changed, despite losing the Government's majority in Parliament.

She told LBC: "I think the UK's negotiating position is as good as it was precisely because this is not just about the UK's position, it's about the interests of the EU as well.

"If you look at the issue of co-operation on security matters, if you look at the issue of trade agreement with the European Union, this isn't just about what's going to be good for the UK.

"I'm fighting for what's good for the UK, but I think what's good for us is also good for the EU and I think that's why this is a negotiation of two sides, coming together to find a way through a process that hasn't been used before, of a country leaving the European Union but doing it in a way that retains that co-operation, retains that partnership, because we're not leaving Europe, we're leaving the EU."

Mrs May will chair the first meeting of a new business council on Thursday to increase the involvement of leading firms in the the Government's Brexit strategy.

Chancellor Philip Hammond and Business Secretary Greg Clark will also be at the Downing Street meeting with a number of company bosses, including Tesco's Dave Lewis, Sir Roger Carr from BAE Systems and National Grid chief executive officer John Pettigrew.

British officials are understood to be bristling at suggestions that they are underprepared for the talks, which have come amid a damaging Cabinet row over the shape of Brexit at home as senior ministers apparently seek to exploit the PM's diminished authority.

On the main battleground over the so-called Brexit "divorce bill", negotiators are frustrated at the inability of the EU to set out in detail what it thinks Britain's legal obligations are, while Brussels officials want the UK to be clearer about what it believes is necessary to settle the accounts.

Insiders close to the talks said EU staff have been surprised at how prepared the UK side was on the detail of the issues.

Meanwhile, on day three of the talks it emerged that the UK has reportedly made clear to the EU that it has the right to send radioactive waste back to Europe after Brexit, as the Government seeks to reach agreement on civil nuclear regulation.

The right of the UK to return processed radioactive waste to its country of origin is highlighted in the Government's four-page position paper on nuclear materials and safeguarding issues.

According to the Financial Times, negotiators hope raising questions over what happens to the nuclear waste, some of which originates from EU countries, will spur on their Brussels counterparts to be co-operative on finding a solution on regulation.

Britain's desire to leave Euratom, Europe's civil nuclear regulator, has sparked some Tory disquiet while opposition parties have made clear their objections to the decision to leave.

Former business minister Pat McFadden said ministers appear to have made incorrect statements suggesting that the supply of radioactive isotopes used to diagnose and treat cancer was not covered by Euratom.

The Labour MP said: "Last week the Government claimed their dogmatic decision to leave the Euratom treaty would have no impact on cancer treatment.

"But we have now had a litany of expert statements from medical bodies saying this is not the case, that these crucial materials do come under the auspices of the Euratom treaty and that without suitable new arrangements being in place there could indeed be an effect on crucial and time-sensitive movements of these materials.

"Either these important medical voices are wrong or ministers have got this wrong.

"They must say now what they are going to do to ensure there is no disruption to the supply of these materials."

The Department for Business, Energy and Industrial Strategy said the issue of nuclear material "is about legal ownership, not physical location" and that talks will seek to resolve "ownership issues".

On Wednesday, European Commission sources also confirmed that its Brexit team's offices are protected by fingerprint scanners, tighter security measures than those deployed at any other department, which are accessible for staff with approved passes.

According to the Telegraph, the ramping up of security comes amid fears of British spying in Brussels, which is believed to be an espionage hotspot, with the EU, its 28 member states and Nato all having a significant presence in the Belgian capital.

The main focus of Wednesday's talks were citizens' rights and privileges and immunities afforded to EU diplomats.

Both sides have remained tight-lipped about the discussions, but Brexit Secretary David Davis will return to Brussels on Thursday and is expected to hold a press conference alongside commission chief negotiator Michel Barnier.