British Prime Minister Theresa May has said the UK faces a "defining moment" as it leaves the European Union, as she prepares to begin the formal Brexit process.

Legislation allowing the prime minister to start the process cleared Parliament last night and Mrs May told MPs she would come to the Commons later this month to announce when she has taken that step.

Mrs May said the legislation would receive royal assent within the "coming days", allowing her to keep to her promise of starting the Brexit process by the end of March.

But in a Commons statement following last week's European Council, Mrs May was jeered by opposition MPs as she stressed her desire to see the single market strengthened because her Brexit plan involves leaving it.

Setting out the next steps in her plan, Mrs May said: "We remain on track with the timetable I set out six months ago, and I will return to this House before the end of this month to notify when I have formally triggered Article 50 and begun the process through which the UK will leave the European Union.

"This will be a defining moment for our whole country as we begin to forge a new relationship with Europe and a new role for ourselves in the world.

"We will be a strong, self-governing global Britain with control once again over our borders and our laws."

"We will use this moment of opportunity to build a stronger economy and a fairer society, so that we secure both the right deal for Britain abroad and a better deal for ordinary working people at home."

Mrs May's plan for Brexit would mean leaving the single market and seeking a comprehensive trade agreement instead.

The prime minister was forced to pause to allow the noise in the Commons to die down as she set out her support for "further steps to complete the single market and the digital single market" and the EU trade deal with Canada.

She said she had pressed for an agreement with Japan in the coming months, adding: "These agreements will lay the foundation for our continued trading relationships."

Mrs May said: "At the same time, we will also seize the opportunity to forge our own new trade deals and to reach out beyond the borders of Europe to build relationships with old friends and new allies alike."

Labour leader Jeremy Corbyn said the passage of the European Union (Notification of Withdrawal) Act was a historic step and Article 50 would start a "process that will shape this country's future".

He warned: "There is no doubt that if the wrong decisions are made we will pay the price for decades to come.

"So now, more than ever, Britain needs an inclusive government that listens and acts accordingly.

"However, all the signs are that we have a complacent government - complacent with our economy, complacent with people's rights, and complacent about the future of this country."