Northern Ireland’s Chief Constable has asked the Northern Secretary to review the Parades Commission determination which ruled the controversial Orange Order march at Drumcree could go ahead, it is understood.

The parade, on September 27th, was blocked by protesters on the mainly nationalist Garvaghy Road and did not go ahead, and a stand-off between the two sides is continuing.

A judgement in the latest court challenge to the Parades Commission determination is due to be delivered at the Court of Appeal in Belfast on Monday.

Chris Bryant has the power to intervene and quash the Parades Commission’s decision, but has so far declined to do so.

The Orange Order has warned of “serious consequences” if Bryant stopped the march.

DUP MP Carla Lockhart said on Friday she expected Bryant would “most likely allow for the court hearing” and reiterated her concerns that “the lawful people … seem to be cast to the side, and the lawbreakers are being rewarded”.

Earlier on Friday it emerged that Northern Ireland’s First Minister, Michelle O’Neill, is to be interviewed by police in relation to her participation in a protest which blocked an Orange march in Portadown.

In a statement on Friday afternoon, O’Neill – who is also the Sinn Féin vice-president – confirmed she had “received a letter inviting me for a police interview in relation to a peaceful protest on the Garvaghy Road.

“I will co-operate with the investigation.”

She said that “for the last two weeks, I have stood in solidarity with the Garvaghy Road residents as attempts were made to force an unwanted Orange march through their community.

“I will continue to stand with the Garvaghy Road residents who should be allowed to live in peace and free from sectarian intimidation” because “it is always right to stand up for what is right and there can be no going back”.

Earlier, Sinn Féin president Mary Lou McDonald had told reporters at a press conference on the nationalist Garvaghy Road that she had not received a letter, but expected to.

On Thursday, a senior PSNI officer confirmed the service was issuing letters to those “reasonably suspected” of having committed a criminal offence in relation to the ongoing stand-off in Portadown, which is now in its 13th day.

The Irish Times has seen a copy of one of the letters, which informs the recipient that “it is reasonably suspected that you may have committed offences” linked to the protest against the Orange parade in Portadown, and invites the recipient to a “voluntary interview under caution”.

Sinn Féin Senator Conor Murphy, and MLAs John O’Dowd (Minister for Finance in the Northern Assembly), Gerry Kelly and Deirdre Hargey have received them.

“There will be processes now, legal processes, investigative processes that will be under way, and of course, just like every citizen, of course we are subject to the law, and we will co-operate with it,” McDonald said.

She reiterated her party’s call on Northern Secretary to step in to resolve the dispute, saying she had spoken to him on Friday morning “urging him again to act”.

People Before Profit MLA Gerry Carroll said on Thursday he had been invited by police to attend a voluntary interview under caution in connection with the protest.

It is understood that, as of Friday afternoon, no SDLP members had received letters.

SDLP leader Claire Hanna told The Irish Times she recognises that she may receive such a letter in the coming days.

A statement said she would “always be accountable for her actions and will engage fully with any policing or judicial process”, but “when faced with a choice between standing with the Garvaghy Road community or doing nothing, she is clear that she made the correct decision”.

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This year was the first time in 28 years that the march, which in the 1990s sparked serious violence which led to more than 20 deaths, was given permission to proceed by the Parades Commission, the body which rules on applications for marches in Northern Ireland.

The decision has been the subject of multiple legal challenges, and the latest judgment is expected in the Court of Appeal next week.

The Garvaghy Road protest was not notified to the Parades Commission, and as an “unnotified” parade is therefore deemed illegal.