Sir Keir Starmer is planning a trip to visit French President Emmanuel Macron in Paris next week.
Nigel Farage told GB News that the visit will allow Macron to privately gloat about a better relationship with pro-EU Labour in the wake of Brexit.
He is expected to meet the French leader in the Elysée early next week.
This comes as part of an attempt by the opposition leader to look like a prime minister in waiting and appear statesmanlike.
Farage said the visit will be used by Starmer for political leverage, but will not change anything in practice.
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Farage told GB News: "Starmer gets to play the role of leader in waiting, prime minister in waiting. So politically for Starmer it achieves quite a lot.
"And for Macron, it says 'We don't really like those nasty Conservatives because they supported Brexit. Those nasty Conservatives who gave us Brexit are leaving and now we've got a nice pro-EU leader who I'm sure we can do business with.'"
He said the visit will be used by Starmer for political leverage, but will not change anything in practice.
Farage warned that, electorally, it "puts Rishi Sunak in a very difficult place".
He explained: "Starmer will return and say he can do a deal with the EU on small boats crossings, and solve the channel migrant crisis. But of course none of that is true in the long term.
"It will allow Starmer to say, 'I'm sure a Labour Government can come to a deal on boats, improve relations with the EU and ease customs."
"In electoral terms, it puts Rishi Sunak in a very difficult place, because he has pledged to stop the boats."
"I don't think long term it will change anything at all, but that's not the point, this is about perceptions."
Catherine Haddon from the Institute for Government think tank told Politico it is "not abnormal" for an opposition leader to make a visit like this, but she said it is "interesting" that Macron has decided to go ahead with the visit.
She said: "It’s not abnormal for opposition leaders to do this, at least not in run-up to an election.
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The visit will put Sunak in a difficult position politically
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"The calculation is between looking like you are an alternative government-in-waiting, versus looking presumptive.
“Starmer and his team clearly feel it works for them, and France is an important country to have a relationship with.
"But still, what is interesting in this is not that Starmer is doing this, but that Macron is."
