SCOTLAND faces a potential farming “subsidy war” with England, which would endanger the Union, Theresa May’s deputy has suggested.

Damian Green, the First Secretary of State, warned that, unless a UK-wide framework was maintained post-Brexit for agriculture, then different nations across the country could begin to subsidise their farmers unfairly, which would put others at a disadvantage and would compromise the integrity of the UK’s single market, sparking a trade war across Britain.

Mr Green’s warning came as Jean-Claude Juncker, the European Commission President, claimed the European Union had the “wind back in its sails” and Britain would “soon regret” its decision to leave.

Analysis: Jean Claude-Juncker will forever be known as the 'Brexit President'

Downing Street announced the Prime Minister is to travel to Florence next week to give a keynote speech on the UK Government’s plans for the post-Brexit transition period in what is being seen as a bid to break the talks’ deadlock in Brussels.

In an interview with the Politico website, Mr Green pointed to how the greatest difficulty over Brexit might occur not in London but with the devolved administrations in Edinburgh and Cardiff.

He explained: “All the devolution settlements were created while we were a member of the EU and when they were being written, none of the various governments, which wrote them thought: ‘Well, what happens if?’ There is just no provision in the devolution settlements for leaving the EU.

“We must ensure the benefits of free trade around the UK, which we’ve all taken for granted, because we are one country, are preserved after Brexit because a lot of the rules about trade have been operated at a European level rather than at a UK level.”

Analysis: Jean Claude-Juncker will forever be known as the 'Brexit President'

He added: “Agriculture is clearly an area where most of the rules were set at European level but those that weren’t are devolved down and we want to continue that.

“We need to make sure that we don’t have subsidy wars to try to help sheep farmers, some in Scotland and some in Wales and so on.”

Last year, British farmers received £2.8 billion in EU subsidies with Scottish ones getting £423 million, more than 15 per cent; much more than Scotland’s general population share of nine per cent.

While the UK Government has pledged to continue the current system of subsidy to 2020, there are no details about how it would work thereafter.

Analysis: Jean Claude-Juncker will forever be known as the 'Brexit President'

Over summer, Michael Gove, the Environment Secretary, spoke of creating a “green Brexit,” whereby farm subsidies would have to be earned rather than merely handed out with pay-outs contingent on farmers agreeing to protect the environment.

The Scottish and Welsh Governments have made clear that unless Mrs May changes her flagship EU Withdrawal Bill, then they could not recommend Holyrood and Cardiff Bay giving their consent. They believe Whitehall is intent on a power-grab.

But while Mr Green and his colleagues have insisted they will give Scotland and Wales more powers post-Brexit, they want first to ensure UK-wide frameworks are in place so that the country’s single market is not jeopardised by different rules and systems operating across the different nations.

A spokesman for Michael Russell, the Scottish Government’s Brexit minister, said: “Devolved powers currently operated at EU level must be returned to Edinburgh, not Westminster, in line with what people across Scotland voted for in the 1997 referendum.

“We are not opposed in principle to common UK-wide frameworks but that must be by mutual agreement and not by imposition. As they stand, the UK Government’s proposals are a blatant power-grab and we cannot recommend that the Scottish Parliament gives its consent,” he added.

In Brussels, Mr Juncker, in his State of the Union address, unveiled his personal vision of a stronger, more united and more democratic Europe.

Analysis: Jean Claude-Juncker will forever be known as the 'Brexit President'

He spelled out closer ties on currency, banking, borders and defence across the 27 states after Britain had left.

“Ten years since crisis struck, Europe's economy is finally bouncing back and with it our confidence. Our EU27 leaders, the Parliament and the Commission are putting Europe back in our Union,” declared the Commission President.

He suggested extending the Euro and the Schengen travel areas to all member states and introducing what would amount to a new finance and economy minister for the entire bloc, allowing more centralised policy-making.

Guy Verhofstadt, the European Parliament’s chief Brexit co-ordinator, suggested Mr Juncker was not going far enough.

The Belgian liberal stressed that the Commission President was able to talk greater integration because of a succession of defeats for the far-right and anti-EU parties across Europe; from Austria to the Netherlands and France.

Analysis: Jean Claude-Juncker will forever be known as the 'Brexit President'

Even politicians like Hungary’s Viktor Orban and France’s Marine Le Pen, he said, had given up on leaving the EU after seeing the problems emerging in the UK. “The only one who does not get it is Mr Farage,” he declared.

The former Ukip leader, who sat grinning behind a tiny Union flag as Mr Juncker spoke, later described the Commission President’s address as "the most open, honest and truly worrying" speech he had heard in his time as an MEP.

He told the Parliament: “All I can say is: thank God we're leaving.

"You have learned nothing from Brexit. If you had given Cameron concessions, particularly on immigration, the Brexit vote - I have to admit - would never, ever have happened.

"And yet the lesson you take is that you are going to centralise and move on to this very worrying, undemocratic union," added Mr Farage.