LONDON, April 8 (Xinhua) -- As British Prime Minister Theresa May held individual phone talks with leaders of European Union states Monday, negotiations to find a Brexit breakthrough resumed between her Conservative government and the main opposition Labour Party.

The stakes have been raised in the quest to agree a deal between the two big political parties in Britain as a Friday departure deadline date looms.

Downing Street said government ministers had contacted the opposition Labour Party to pave the way for technical discussions Monday evening.

But Labour leader Jeremy Corbyn complained talks between both sides have so far yielded no change in May's so-called red lines. Labour wants May to agree a deal that keeps Britain linked to the European Customs Union.

Media in London quoted sources close to the government indicating May had not accepted Labour's customs union demand, while pro-Brexit Conservative politicians fear such a link would undermine Brexit.

Corbyn said: "The exchanges with the government have been serious, but our shadow cabinet expressed frustration that the prime minister has not yet moved off her red lines so we can reach a compromise."

An emergency summit of European Union member state leaders takes place in Brussels Wednesday where May is expected to detail fresh plans aimed at ending the impasse in the British parliament.

Her aim is to win support to agree to an extension of Britain's departure date until June 30.

On Tuesday May travels to Europe for separate talks with German Chancellor Angela Merkel and French President Emmanuel Macron in Berlin and Paris respectively.

It is part of May's plan to speak with all 27 European leaders ahead of Wednesday's crunch summit meeting. May also spoke Monday with European Commission President Jean-Claude Juncker.

In the unelected House of Lords, politicians Monday night backed the bill introduced in the House of Commons by Labour MP Yvette Cooper to prevent Britain leaving the EU with no deal.

The leader of the House of Commons Andrea Leadsom told MPs that if the bill receives Royal Assent from Queen Elizabeth there will be a government motion Tuesday asking the British Parliament to approve the May's request to the EU to delay Brexit.

Across the Irish Sea, talks took place Monday in Dublin between Irish Prime Minister Leo Varadkar and the EU's chief Brexit negotiator Michel Barnier.

Speaking later to journalists, Barnier said the EU could be much more ambitious in the future trade relationship if Britain were to drop its red lines.

Barnier welcomed May's decision to hold cross-party talks with the main opposition Labour Party, adding: "There are intensive cross-party discussions happening in London as we speak. We all hope these talks produce a positive outcome. I have said many times before that we can be much more ambitious in our future relationship with the UK."

"The political declaration allows for a range of outcomes, including a customs union. We are ready to make this clear if it helps and the work can be done extremely quickly."

Varadkar said he and Barnier exchanged views on the length of a possible extension for Britain.

He said: "I look forward to discussing it further with my EU counterparts at the European Council on Wednesday. There will be of course different views but I am confident we can reach agreement."

Britain also started making formal arrangements Monday for the country to take part in next month's European Parliament elections, but the government said it hoped a Brexit deal could be reached to avoid Britain having to elect Euro MPs (MEPs).