Conservative MP Sir Bill Cash said the Prime Minister was right in opposing the terms and conditions for the negotiations "imposed" by Brussels, who he said had failed to accept the sovereignty of the UK.
It comes after the first week of Brexit talks between the EU and the UK, which saw Britain baulk at being asked to follow EU rules.
Speaking at the The Bruges Group Conference in London, Stone MP Sir Bill backed the Government's stance in the early stages of the negotiations.
"At last – after being shackled to the EU for 47 years – we have regained our freedom," he said.
"The Government is rightly refusing to accept the terms and conditions that the EU wants to impose on the UK in these negotiations, and to which the previous Government capitulated.
"The EU is undemocratically refusing to face the fact that we have lawfully left the Union and that this was based on the votes of the British people in the referendum itself and endorsed in the December 2019 General Election.
"They therefore also refused to accept the sovereignty of the UK.
"They will discover during these negotiations that the UK’s political will and the sovereignty of the Mother of Parliaments, with the courageous determination of the Prime Minister, will prevail, as it has for centuries.
"This is Boris Johnson’s Churchill moment. We have saved ourselves and Europe many times and will do so again."
Michel Barnier, the EU’s chief Brexit negotiator, last week warned of "very, very difficult" areas of disagreement with the UK following the first round of talks.
He said there were four areas of "very serious divergence", including fishing rights in UK waters, the role of the European Court of Justice, Britain’s unwillingness to align with EU rules, and how any future deal is policed.
Both parties have pledged to work intensively to reach an agreement by the end of this year, when the UK's post-Brexit transition period is due to end.
At that point the country is set to leave the single market and the customs union.