BELFAST, April 9 (Reuters) – Less than two decades after a U.S.-brokered deal brought peace to Northern Ireland, British Prime Minister David Cameron may have to go cap in hand to one side of the sectarian divide if he wants to keep power after the May 7 election.

Northern Ireland’s Democratic Unionist Party (DUP), whose combative British nationalism was forged in the Protestant ghettos of 1970s Belfast, is promising voters the opportunity of holding the balance of power in the United Kingdom.

But that prospect is making some uncomfortable among mainly Catholic Irish nationalists in a country where even a slight shift in the balance of power can fuel tensions on the streets.

In the most unpredictable British election in recent times, neither the Conservatives nor Labour are expected to win a majority in the 650-seat parliament while the DUP is targeting nine seats.

“This opportunity may not come around again for a political lifetime,” DUP leader Peter Robinson told British flag-waving supporters last month when he unveiled a list of concessions the party wants in exchange for its support.

The DUP has said it is also open to a deal with Labour, but analysts say that is much less likely due to the DUP’s social conservatism, euroscepticism and championing of defence spending.

While some in England are uncomfortable at how a possible deal between Labour and the Scottish National Party might give 5 million Scots influence over 54 million people in England, success for the DUP could put Northern Ireland’s 1 million Unionists at the centre of Britain’s government.

“We’d be nervous,” said Joseph Donaghy, 20, a member of Irish nationalist party Sinn Fein, who said members feared the DUP could become “Tory lapdogs” backing austerity, or push their more conservative social agenda on abortion and gay rights.

BELFAST DIVIDED

Seventeen years after a peace deal ended three decades of violence in Northern Ireland, politics remains sectarian with 17 of 18 seats in London held by either Irish nationalists, mainly Catholics, who favour a united Ireland, or by predominantly protestant pro-British unionists.

“This country’s different … We’re in ghettos still,” said Walter McBride, a 48-year-old youth worker from the Shankill Road area of West Belfast, where election posters are emblazoned with British flags and the orange of Ulster Protestantism.

Like most of a dozen voters questioned by Reuters, he thought his community would benefit if the DUP supports the next government.

On the other side of a six-metre fence, where posters on the Falls Road are decorated in the colours of the Irish flag, most said a DUP-supported government would not be good for them.

While most of the DUP’s 100-point wish list is non-sectarian, several elements would likely be opposed by nationalists.

It calls for a scrapping of welfare benefits for “perpetrators” of armed attacks and for members of parliament who refuse to take their seats at Westminster – both of which would impact Sinn Fein members.

It also mentions the regulation of contentious unionist parades and looks for protection in law for the official display of the British flag.

When Irish nationalists secured a majority in Belfast city council in late 2013 for the first time and limited the display of the flag over City Hall, the shift in power shocked some unionists and sparked some of the worst street violence in the province in years.

The DUP’s advantage in Westminster is magnified by Sinn Fein’s century old boycott of seats in the British parliament, whose jurisdiction it rejects.

PRICE OF POWER

Meeting the DUP’s demands for concessions for Northern Ireland could be tricky for a Conservative government if they are seen as coming at the expense of the other countries of the union.

In an interview with Reuters, Robinson refused to be drawn on DUP party candidates referring to a windfall of up to 1 billion pounds of extra funding for Northern Ireland from London through supporting the next government, saying the party did not want to be encumbered by “some vulgar figure.”

But his list of issues to be discussed as part of any agreement included increased spending on health and education in Northern Ireland and “more satisfactory terms” for a planned devolution of corporation tax to the province.

Another area that might disconcert some English voters are the DUP’s social policies.

DUP legislators have backed the right of a Belfast bakery to refuse to make a cake with a gay rights slogan and proposed a law that to allow religious business people to refuse to serve people where that would conflict with their religious beliefs.

At least one senior party member has defended creationism, the theory that the world was created by God 10,000 years ago.

Robinson said this would not be a difficulty as “moral issues” tended to be dealt with in free votes in parliament. In any case, parties did not have to like the DUP to do a deal.

“If one of the national parties … needs the votes of the Democratic Unionist Party to give them the necessary numbers, they will learn to like the Democratic Unionist Party a great deal,” he said with a smile.

While Cameron says he is seeking a majority and refuses to discuss any possible alliances in the event of a hung parliament, current forecasts show he is likely to win significantly less than the 323 seats needed for a majority.

If Cameron fails to win a majority, the anti-European Union UK Independence Party has said it and the unionists could form an alliance with the Conservatives.

“The DUP have been the forgotten part of this equation,” UKIP leader Nigel Farage told Reuters. “There would be some points of agreement between us and the DUP.” (Additional reporting by Kylie MacLellan; editing by Guy Faulconbridge and Giles Elgood)