But Jarosław Kaczyński, who leads Poland's conservative Law and Justice (PiS) party, concedes that the EU would have to 'radically change' in order for Britons to want to return.
The former Prime Minister said that the "idea for today... foresees efforts aimed at making Britain return", which included a second referendum.
"Britain today risks falling apart," he said.
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Kaczyński is the first European leader to make an outright call for a second referendum.
In contrast, other leaders, such as Commission President Jean-Claude Juncker, have pressured London for a speedy divorce.
His comments were echoed by Austrian EPP group MEP Paul Rübig, who called for another referendum on a "united Great Britain within EU."
The consequences, he said, was a "Little England without London and Scotland."
In another development, a French Mayor has called for Brussels to ditch its use of the English language after Britain voted to leave the EU.
English is one of 24 official languages of the EU and is also one of the working languages used to conduct everyday business.
But Robert Ménard, the Mayor of the southern French town of Béziers, believes English now no longer has "any legitimacy" in Brussels in the wake of the Brexit vote.
Elsewhere, the left-wing French presidential candidate, Jean-Luc Mélenchon, said English can no longer be the "third working language of the European Parliament."
An estimated 51 per cent of EU citizens can speak English as a first or second language while just over a quarter can speak French and nearly a third can speak German.
It has also been reported that the Commission has received 'thousands' of emails from Britons since Friday saying they were unhappy with the result, including some from people who had voted to leave the EU and were now regretting it.
Meanwhile, within just hours of the UK's Brexit referendum vote, the Mayors of several communes in and around Brussels reported a surge in British residents seeking information on how to obtain Belgian citizenship.
In Waterloo, where there are 450 registered Britons, Mayor Florence Reuter told Le Soir that five people had submitted the paperwork to begin the procedure on Friday morning. Dozens of others had called in to ask for information. "The registry office has dealt with nothing else this morning," she added.
Woluwé-Saint-Pierre received three submissions on Friday - having received none at all from British residents in the past four months. There were two requests for info at Brussels city hall, where 1200 British citizens are on the population register.
Olivier Deleuze, Mayor of Watermael-Boitsfort, said he had three Britons on Friday morning asking to begin the procedure to become Belgian. "It's exceptional," he told Le Soir. "Normally we never get this sort of request. We had one in 2013 and one back in March."
Britain's decision to leave the EU "adds a new level of uncertainty" for British firms doing business in Belgium, the British Chamber of Commerce in Belgium has warned.
Belgium is the seventh largest export market for the UK and has a big British business community.
A chamber spokesman said: "A deal needs to be found. As the Chamber we advocate for as short as possible negotiating period and as clear as possible an outcome. It's all about clarity. The longer this period of negotiation lasts the less good it is for businesses to invest in the EU. This vote adds a new level of uncertainty."