The Police Service of Northern Ireland must charge or release Sinn Fein leader Gerry Adams on Sunday night – with party sources confident he will be freed after four days of questioning over the Jean McConville murder.

Adams has been questioned for up to 17 hours a day since he voluntarily agreed to assist with police investigations into the 1972 murder by the IRA of the mother of 10.

The Sinn Fein deputy for Louth has consistently denied any involvement in the abduction and murder of McConville whose body was eventually found in 2003, on a beach in County Louth 50 miles from her Belfast home.

The BBC website reports that police have until 20:00 BST on Sunday to charge or release Adams.

But a Sinn Fein source has told the BBC that ‘there would need to be a significant development’ for a charge.

The website reports that if charged, Adams would appear at a special court sitting on Sunday or Monday.

A judge gave police an extra 48 hours to question Adams on Friday and the PSNI can request a further extension of the detention order.

His Sinn Fein colleague Martin McGuinness has again accused elements of the Police Service of Northern Ireland of settling ‘old scores’ with the arrest of Adams.

Speaking at a protest rally in Belfast, Northern Ireland’s deputy first minister McGuinness said Adams’s arrest was part of an effort by some police officers to ‘settle old scores whatever the political cost’.

McGuinness referred to ‘an embittered rump of the old RUC, the Royal Ulster Constabulary’. The RUC was replaced in 2001 by the Police Service of Northern Ireland.

He added: “Allegations contained in books and newspaper articles which the PSNI are presenting to Gerry as evidence that he was in the IRA in the 1970s have been around for 40 years.

“But they are only now trying to use these. Is this not political policing?

“This is a replay of the failed effort in 1978 to charge Gerry with membership of the IRA.”

McGuinness suggested on Friday that Sinn Fein may look again at whether it would continue to support the PSNI.

Sinn Fein has claimed the arrest was deliberately timed three weeks ahead of local and European elections.