Brandon Lewis could override the Northern Ireland executive and directly instruct the nation’s health trusts to provide abortion services, warning leaders in a leaked letter that the continued delay is unacceptable conduct in public office.

The Northern Ireland secretary wrote to the first minister, Paul Givan, and his deputy, Michelle O’Neill, warning he would soon “have no alternative but to take further steps to ensure that women and girls have access to abortion services as decided by parliament, and to which they have a right”.

The Guardian understands the Northern Ireland Office could explore working directly with health trusts to implement the abortion provision if Stormont does not take steps to ensure they do so. Lewis warned in his letter that continued failure could leave Stormont in breach of the European convention on human rights.

In a separate letter to the health minister, Robin Swann, Lewis demanded to see a detailed assessment of progress to date and a roadmap to meeting the March 2022 deadline. He said NIO officials had been blocked from attending meetings with the department – which he called “unacceptable.”

Abortion was decriminalised in Northern Ireland in October 2019 after a Westminster vote led by the Labour MP Stella Creasy. But since Northern Ireland’s Department of Health has not commissioned or funded any services, leaving some trusts to try to provide a service without funding or a framework.

Previously in Northern Ireland abortions were allowed only if a woman’s life was at risk or if she was at risk of permanent damage to her mental or physical health. It meant in most cases that women seeking the service were forced to make sometimes traumatic journeys to England, risking prosecution.

Earlier this year, Lewis said he would take unprecedented action and use parliament to give himself new powers to commission the services. Stormont has been formally directed to commission the services before the end of March 2022, but there has been little material improvement.

A high court judge ruled this month that Lewis had failed to uphold his duties to provide full abortion services in Northern Ireland after a judicial review was brought by a woman told to travel to England for an abortion during the pandemic.

Lewis said earlier he was disappointed in the ruling, adding that he had been the only party to take steps to try to force the executive to provide the services.

In the letter leaked to the Guardian, Lewis warned Givan and O’Neill he was prepared to take further unprecedented intervention in Northern Ireland’s health service, saying it was “entirely unacceptable” to attempt to block a legal duty.

“I firmly believe that there is also a moral duty to women and girls to ensure they are afforded their fundamental human rights – the same rights afforded to women and girls in the rest of the UK,” he wrote.

“The executive cannot continue to delay in this matter and the court could well conclude that a decision not to agree to proposals for the commissioning of services breaches article 8 of the ECHR.”

Lewis said he agreed with the judge who called the delay “dispiriting”.

“In fact, I would go further. Those in public office must comply with their legal obligations whether or not they agree with the law in question,” he wrote in the letter.

Lewis said if it became “clear to me” that the Department of Health or executive were “not making sufficient progress, or are intent on blocking this issue, I will have no alternative but to take further steps to ensure that women and girls have access to abortion services as decided by parliament, and to which they have a right”.