French opposition leader François Hollande meets Ed Miliband. Reuters/Press Association

François Hollande, the leftwing French presidential frontrunner, is to stage a high-profile campaign visit to London aimed at boosting his international profile and explaining his drive to rein in the excesses of world finance.

The former Socialist party leader, who has never served in government, is engaged in an increasingly bruising election fight with Nicolas Sarkozy before the first-round vote in April. The world diplomatic stage has become a battleground for the campaign since the German chancellor Angela Merkel's open support for Sarkozy followed by David Cameron's "good luck" message to the French incumbent at a summit in Paris earlier this month.

By choosing Britain as his first major campaign visit on Wednesday, Hollande will set out his position on the European budget treaty, which he wants to renegotiate. He is also likely to explain what his proposed regulation of world finance might mean for the City.

At a time when the UK is increasingly turning to French atomic energy expertise, Hollande wants to start reducing France's heavy dependence on nuclear power. The increased military co-operation between France and the UK, recently showcased in Libya, has not so far been a campaign issue for Hollande, but he wants to speed up the withdrawal of French troops from Afghanistan.

London has become a crucial campaign destination for candidates in the French presidential race. The UK capital is home to around 300,000 of the 400,000 French people in Britain, a population large enough to be considered politically as France's sixth biggest city. Sarkozy cemented the importance of "Paris-on-Thames" during his 2007 election campaign, staging a London rally urging expats to come home, saying: "France is still your country even if you're disappointed by it."

At a conference at King's College and a rally of the French community in London, Hollande is likely to expand on his drive for more rules for the financial markets and his recent announcement of a 75% tax bracket on annual earnings above €1m. In a book published last week he said unregulated markets had become so powerful that the City of London "weighs so heavily", convincing Cameron to refuse all financial reform. However, some of Hollande's regulation ideas draw on UK proposals such separating investment banking from banks' retail businesses.

Elizabeth Guigou, a former minister and part of his campaign team, said the London visit was also about understanding Britain's reasoning on Europe, including Cameron's refusal to sign up to the new EU treaty.

Hollande had earlier said: "We need Britain to feel part of Europe." But he added that France could never have accepted Cameron's attempt to create a "sanctuary" from financial regulation for the City in the new European treaty.

Hollande's visit starts with a lunch with the Labour leader, Ed Miliband, and the shadow cabinet at Westminster. The Socialist candidate, who unlike Sarkozy says he speaks English, does not know Cameron or Nick Clegg. He has praised Tony Blair on health and education and the length of New Labour's time in office but criticised its economic politics, saying it "succumbed to the dominant idea that the markets could regulate themselves and … we saw the consequences."

Hollande is not expected to meet financiers, unlike Sarkozy, who made a high-profile speech in the City on a state visit in 2008.

The stakes for a London campaign trip are even higher this year because of electoral changes. For the first time in legislative elections in June, the 2.5 million French expats will be able to vote for their own MPs in overseas constituencies. The new MP for northern Europe will represent French people in the UK, Ireland, Scandinavia and the Baltic states. The majority of French expats voted for Sarkozy in 2007. In London, French expats are considered to lean to the right, but turnout tends to be low with only 30% voting in 2007.

Axelle Lemaire, the Socialist candidate for MP for northern Europe, told the Guardian last year that the French community in London was more than the stereotype of rich traders. "French people living in the UK are young, the majority under 40, there are more women than men. One third work in the public sector, especially in education. The idea of lots of French bankers in the City is only part of the picture."

James Shields, professor of French politics at Aston University, said London visits were so important to French presidential candidates, "first, for the high-profile stage on which to project their claims to international statesmanship", and particularly for Hollande "to cut a figure beyond France". He added the visit would allow the Socialist candidate "to play to a wider gallery than his natural leftwing base".