Jeremy Corbyn has said it is "unconscionable" for elected politicians to have no say in major decisions in Northern Ireland as he called on the Stormont parties to come together to resurrect devolution.
The Labour leader visited Londonderry in the North West on the second day of a two-day trip to learn more about how Brexit affects the country.
Recently a civil service decision to approve a major incinerator project in the continued absence of powersharing ministers was overturned by the courts.
Mr Corbyn said: "It is unconscionable that you have civil servants making major decisions, then challenged by the courts, with elected politicians having no say whatsoever."
Stormont has not sat for months following a dispute over a botched green energy scheme.
The Labour leader attended a business breakfast in Londonderry on Friday.
He said he was seeking a customs partnership with the EU to ensure there were no regulatory barriers after Brexit.
"Any kind of border, physical border, virtual reality border, technological border, whatever, would be very damaging to the economy," Mr Corbyn said.
He said it would threaten the progress and direction of travel since the end of the conflict and the signing of the Good Friday Agreement.
On Thursday, Mr Corbyn insisted he was not advocating or asking for a referendum on Irish unity.
The Labour leader said if he was to become prime minister, he would only trigger a border poll in line with the terms of the Good Friday Agreement - which stipulates a vote can only be called if there is evidence that a majority in Northern Ireland would support reunification.
Mr Corbyn, who in the past made no secret of his support for a united Ireland, was pressed on the issue on his first visit to Northern Ireland as Labour leader.