Labour today promised to get behind Britain's exit from the European Union, saying they now believed Brexit is an enormous opportunity for the country.

Shadow chancellor John McDonnell said that Labour would not seek to prevent or delay Brexit, labeling those trying to do so as being "on the side of certain corporate elites".

He told a meeting in central London that Labour "must not try to re-fight the referendum or push for a second vote,"

"If Article 50 needs to be triggered in Parliament, Labour will not seek to block or delay it," he said.

He added that: "to do so would put us against the majority will of the British people and on the side of certain corporate elites, who have always had the British people at the back of the queue."

In a shift from Labour's previous support for the EU, McDonnell said he believed it had been run in the interests of big business.

"While Labour supported remaining in the EU to protect workers’ rights, we cannot hide from the fact that too much of the EU also had aspects of the old model, putting the interests of big business over ordinary people," he said.

"Labour accepts the referendum result as the voice of the majority and we must embrace the enormous opportunities to reshape our country that Brexit has opened for us."

He insisted that the party needed to change their attitude about Brexit

"It is time we all were more positive about Brexit," he said.

McDonnell was asked how Labour could have any influence over the Brexit process when he had just ruled out voting against it, or seeking to block it.

He replied that the party would use "moral pressure" to influence the government.

"I think it's the moral pressure that we'll be able to exert… I don't think it will come down to parliamentary procedures…" he insisted

"No government can resist (the moral pressure)."

Labour were accused of "capitualating" on Brexit, following McDonnell's speech.

“Labour’s premature capitulation on Article 50 leaves those of us who oppose a hard brexit in a weaker position," Green Party co-leader Caroline Lucas said.

"As a result we now have less power to persuade the government to give us proper details on their plans ahead of a vote."