EU chief Jean-Claude Juncker warned today that Britain will 'regret' Brexit as he drew battle lines for trade negotiations.

The commission president said the UK had to understand what it 'means' to be outside the bloc and warned against 'cherry picking'.

Mr Juncker also caused fury among British MEPs as he used a speech at the European Parliament to claim that the Irish border was a 'European issue'.

One shouted at him: 'It's a British issue.'

EU chief Jean-Claude Juncker warned that Britain will 'regret' Brexit as he addressed the European Parliament today

Mr Juncker told the session in Strasbourg there was 'increasing urgency' to negotiate the UK's orderly withdrawal from the EU

Mr Juncker was cheered by Eurosceptic MEPs as he noted the UK's departure from the EU was due to happen on March 29, 2019.

Seemingly stung by their applause, Mr Juncker said the time would come 'when you will regret your decision'.

Flanked by EU chief negotiator Michel Barnier, Mr Juncker told the session in Strasbourg there was 'increasing urgency' to negotiate the UK's orderly withdrawal from the EU.

He said he did not want EU citizens to 'fall victim to Brexit' as he stressed the importance of securing their rights.

Mr Juncker said 'cherry-picking is not going to be possible' in the future trade relationship between the UK and EU.

'I would rather have preferred Britain not to have decided to leave the European Union, but anyone who leaves the European Union has to know, frankly, what this means,' he said.

'If you decide to jettison, leave behind, the common agreements and rules, then you have to accept that things cannot remain as they are.'

Despite Theresa May setting out her vision for Brexit in a speech at Mansion House earlier this month, Mr Juncker insisted it was 'obvious' that the UK needed to give 'more clarity on its future relationship with the EU'.

But he warned that the border between Northern Ireland and the Republic could be a major roadblock to sealing a deal.

Mr Juncker said the controversial Brussels legal text demanding full regulatory alignment between Northern Ireland and the EU 'should not come as a surprise' to the UK.

He said it 'translates faithfully' the agreement reached between Theresa May and the EU in December.

Mr Juncker said: 'The 27 member states stand firm and united when it comes to Ireland. For us this is not an Irish issue, it is a European issue.'

Mr Juncker was flanked by EU chief negotiator Michel Barnier during his speech today

Former Ukip leader Nigel Farage said the EU was trying to 'bully' Britain. Federalist MEP Guy Verhofstadt said a deal on citizen's rights was now close

When one MEP shouted 'it is a British issue', Mr Juncker shot back: 'It is all for one and one for all, that is what it means to be part of this union.'

European Parliament's Brexit co-ordinator Guy Verhofstadt also called for more details from the Prime Minister.

He said: 'There was this Mansion House speech by Mrs May, but it was mainly repeating the red lines that we know already.'

The Prime Minister had said 'we cannot accept the rights of Canada and then the obligations of Norway' but 'I don't think that we have ever presented that proposal to the UK side', Mr Verhofstadt said.

'I think the UK side have to understand that the opposite is also not possible - you cannot have the rights of Norway and then the obligations of Canada.'

Mr Verhofstadt said it was time to move beyond 'slogans' and 'soundbites'.

He has put forward a motion to the European Parliament for an 'association agreement' to deal with the future UK-EU relationship.

But it insists on a 'binding interpretation role' for the European Court of Justice (CJEU) and rejects UK efforts to 'cherry-pick' single market access for particular sectors, such as the financial services industry.

Former Ukip leader Nigel Farage claimed the European Commission was trying to 'bully' the UK.

Mr Farage, an ally of US president Donald Trump, said the UK should leave the EU without a transition deal and claimed a transatlantic trade deal could be struck 'in 48 hours'.

He said: 'Mrs May, we did not vote for a transition period, we voted to leave this organisation, we voted to leave the customs union, we voted to leave the single market.

'Please Mrs May, at this summit next week, do what Trump has done - stand strong against the European Commission, against the unelected bullies.'

Theresa May (pictured in the House of Commons yesterday) is negotiating a deal with the EU