Northern Ireland should hold a referendum, possibly as early as 2016, on whether it wants to remain British or become part of a united Ireland, Sinn Fein, the main pro-Irish nationalist party in the province, said on Monday.

The British government in London, which is already facing calls to allow a referendum in 2014 on ending Scotland's 300-year union with England, has the final say on whether a referendum on the future of Northern Ireland can be held.

Martin McGuinness, Sinn Fein's leader in Northern Ireland, said he would like to see a referendum held after the next election for Northern Ireland's assembly, which is likely to happen either in 2015 or 2016.

It could take place anytime between 2016 and 2020/21, McGuinness, and a former commander with the Irish Republican Army (IRA) guerrilla group, told the Irish Examiner newspaper about a possible referendum. I don't see any reason whatsoever why that should not be considered.

Just as 2014 is a key year for Scottish nationalists, marking the 700th anniversary of a historic victory over the English, so 2016 is important for Irish nationalists, as it marks the centenary of a popular uprising against British rule.

Another leading Sinn Fein member echoed the comments made by McGuinness. I do hope the referendum happens in the next term of the assembly government, Pearse Doherty, a member of parliament in the Irish Republic, told Newstalk radio in Dublin. I would suspect that it will.

Most Irish nationalists in Northern Ireland are Catholics. However, it is not clear that all Catholics in the province would want to end the union with Britain and unite with the Irish Republic, particularly when Dublin is struggling to emerge from a deep financial crisis.

The British state is the biggest employer in Northern Ireland and the province's population enjoys a number of benefits, including universal free healthcare, which are not available in the Republic.

The 2001 census showed that 40 percent of Northern Ireland's population classified themselves as Catholic, 46 percent were Protestant and 14 percent said they had no religion. Details of religious affiliation from the 2011 census have yet to be released.

Under a 1998 peace deal that ended the IRA's campaign against British rule of Northern Ireland, if a referendum is approved by London, another one cannot be held for another seven years.

(Reporting by Carmel Crimmins; Editing by Alessandra Rizzo)