Sinn Féin won the most first-preference votes in Saturday’s Irish general election, delivering a shock to the country’s political landscape after decades of domination by the centrist rivals Fine Gael and Fianna Fáil.

However, the fragmented results will produce a hung parliament with no party close to 80 seats, meaning there could be weeks – possibly months – of negotiations between party leaders before a government is formed.

Whatever happens, Leo Varadkar the Fine Gael prime minister who broke the Brexit impasse in a summit with Boris Johnson in the Wirral in October, is unlikely to survive, forcing a new set of politicians on Downing Street and Brussels just as the critical next phase of Brexit talks begin.

Will Irish policies on Brexit change?

All three of the leading Irish parties are pro-EU, and whoever is in government will adhere to the Brexit deal and the Northern Irish protocol, which involves checks along the Irish border.

But Sinn Féin, more than any party, is advantaged by the Brexit deal because Northern Ireland remains a de facto member of the EU single market, pushing it into closer economic union with the republic.

Jonathan Tonge, professor of British and Irish politics at Liverpool University, said: “The more friction there is in terms of Northern Ireland trade, the better for Sinn Féin, although they won’t say that publicly.”

What about unionists in Northern Ireland?

A coalition involving Sinn Féin will spook unionists, who have already accused Johnson of betraying them in the Brexit deal. Such a coalition would “effect unionist insecurity”, said Etain Tannam, professor of international peace studies at Trinity College, Dublin.

What about Brussels?

Michel Barnier has met Mary Lou McDonald and her team on several occasions so Sinn Féin are not an unknown quantity. However, as a nationalist party with policies of the left, “they would face dilemmas given their own ideology in trade talks where they would be rubbing up against neoliberalism”, Tannam said.

Does this bring united Ireland closer?

No. Sinn Féin has said publicly it wants a border poll within five years but, as Tannam points out, that is not in their manifesto. Fianna Fáil and Fine Gael have been loath to do anything explicit on the subject because of the sensitivity. Any such move would be considered an act of hostility towards unionists in Northern Ireland. “The department of foreign affairs, which has been very influential, would be against it,” Tannam said.

How will the result go down in the UK?

Sinn Féin, founded in 1905 before the establishment of the Irish state, has been politically active in Northern Ireland for decades but has refused to take its seats in Westminster.

However, when McDonald took over from Gerry Adams as president, the party redoubled efforts to gain influence in London, in politics and the media.

While Fine Gael and Fianna Fáil have decades of dealing with the Conservative party, Sinn Féin does not, as its long term goal of a united Ireland would in effect break up the United Kingdom.

“Downing Street will not exactly be welcoming this result,” Tonge said.