Foyle MP Elisha McCallion raised the case of Derry republican Tony Taylor during talks at Downing Street on Thursday.
The Derry man was returned to jail in March last year after his early release licence was revoked by then secretary of state Theresa Villiers.
A former republican prisoner, Taylor was sentenced to 18 years in jail in 1994 for IRA activity and for three years in 2011 for possession of a rifle.
Elisha McCallion was among a Sinn Fein delegation which met with British prime minister Theresa May in London on Thursday afternoon.
Speaking to the ‘Journal’ from Westminster, the newly-elected Derry MP said: “I took the opportunity while at Downing Street to present a letter outlining my and Sinn Féin’s objections to the continued imprisonment of Tony Taylor.
“In the letter, I emphasised that the continued incarceration of Tony Taylor following the latest hearing at Laganside Court is a denial of justice and due process and that no evidence has been submitted to justify his continued detention in Maghaberry Prison.
“The quasi-judicial process which occurred is a travesty of justice and has acted in subordination to the political primacy of the NIO.
“Sinn Féin has consistently opposed the power vested in the British Secretary of State where a licence can be revoked without an open and transparent process.
“The refusal to release Tony Taylor raises very serious concerns about political interference in the justice system in the North of Ireland.
“Tony Taylor’s detention continues to be wrong and is a violation of his human rights.
“In the letter, I also impressed on the British Prime Minister the deeply negative implications for society in the North of Ireland that this denial of due process and corruption of the judicial system will have.”
Earlier this week, Tony Taylor’s wife, Lorraine, said a mass rally and judicial review may be the next steps in the ongoing campaign for his release.
The Derry mum-of-three said the continued detention of her husband was having “a devastating impact” on their children.