The government is "misleading" the public by suggesting Britain cannot change its mind on Brexit, the man who wrote Article 50 has said.
Lord Kerr, who authored the document allowing EU member states to withdraw, said the facts were being "inadequately represented, or indeed misrepresented" in the current debate.
During a speech in London for the pro-EU Open Britain campaign, the former UK ambassador to the European Union insisted that the Prime Minister's decision to trigger the withdrawal process did not mean departure was inevitable.
It comes as Theresa May issued a blunt message to pro-EU MPs, saying any attempt to block Brexit would not be tolerated.
Brexit Secretary David Davis said the date of the UK's departure would be included in the EU Withdrawal Bill, and would be set at 11pm GMT on March 29, 2019.
However, Lord Kerr said the two-year time limit for countries to leave once Article 50 had been triggered could be extended if all parties agreed.
He said the time limit for talks, set out in the Article itself, was simply to reassure any member state which did wish to leave the bloc that the would not be tied down by endless negotiation.
He criticised the government for implying that now the letter triggering the process had been sent, there was no going back - saying the public was not being given the full story.
"Intentions can change," he said.
"We still have all the rights of a member state today, including the right to change our minds."
He went on to read statements from EU leaders, including President of the European Parliament Antonio Tajani, and President of the European Council Donald Tusk, which state they would welcome Britain changing its mind on Brexit.