Sir John Major has told those campaigning for Britain to leave the EU to "go to North Korea" if they want "undiluted sovereignty".
The former Conservative prime minister said "splendid isolation" would leave the UK weaker.
And he warned of economic damage if the UK votes to leave in the 23 June referendum.
Vote Leave said Sir John had been "wrong on nearly every EU issue over the last 20 years" and was wrong now.
Speaking on BBC Radio 4's Today programme, Sir John said: "Day after day you have had the Brexit people producing soundbites that are either offensive or inaccurate or just plain silly.
"I don't believe that it is patriotic to argue for a case that is going to make this country weaker and is going to make the wellbeing of this country less certain in the future."
He went on: "To listen to them, you would think we are entrapped in the clutches of an evil empire, not in a democratic partnership with our European neighbours whose sunshine and pavement cafes we enjoy during holiday breaks."
The Leave campaign has said leaving the EU would restore sovereignty to the UK, freeing it from the influence of Brussels and the European Court of Justice, which oversees the application of EU-wide rules.
But Sir John said: "If you want undiluted sovereignty in the modern age, when everybody is interconnected, then go to North Korea because that is where you will get it.
"It is certainly true that we share sovereignty. We take some sovereignty from other people, we share some of ours.
"We haven't surrendered it because, at the end of the day, the House of Commons, our representatives, can say, 'We won't have this, we will leave the European Union.'
"But in the modern world, the modern world of interconnectivity, the modern world with the economy that now exists, you have to share sovereignty or you find yourself isolated and weaker."
Vote Leave chief executive Matthew Elliott said: "John Major complained about soundbites before descending in hyperbole about North Korea without even a hint of self-awareness.
"John Major has been wrong on nearly every EU issue over the last 20 years. He said Britain should join the ERM - that was a disaster which cost 3 million their jobs.
"He signed us up to Maastricht saying it wouldn't give up sovereignty and he refused to rule out joining the euro.
"Now he doesn't want to take back control and stop handing Brussels £350m a week. He was wrong then and he is wrong now."
It comes as UKIP leader Nigel Farage claimed he had been sidelined by Vote Leave, which is the officially designated campaign to get Britain out of the EU.
He said in a speech that Vote Leave was on the "back foot" because it had failed to focus on immigration - but it had rejected his offers of help.
"Every time I attempt to work with them I am rebuffed and rejected," he added.
A Vote Leave spokesman said: "We wish Nigel well."
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