A UNITED Nations independent expert on the promotion of democracy has said that the change of government in Madrid gives hopes that negotiations can begin on a new independence referendum for Catalonia.

Alfred-Maurice de Zayas said that “a modicum” of historical knowledge should be enough to help outsiders understand that Catalans have their own distinct culture and traditions and that a new poll is “the only way forward”.

During the campaign that led to last October’s referendum, the heavily politicised Spanish courts ruled that such a poll was illegal under the constitution.

However, writing on his blog, de Zayas said there was no need to change the Spanish constitution to allow the vote: “The right of self-determination is fully integrated and in force in the Spanish domestic legal system.

“It is not necessary to modify the Spanish constitution in that respect.

“The principles relating to the fundamental rights and liberties recognised by the constitution shall be interpreted in conformity with the Universal Declaration of Human Rights and the international treaties and agreements thereon ratified by Spain.

De Zayas continued: “In accordance with the Spanish constitution, the right of self-determination must be applied in Spain in line with the provisions of international law ... In this regard, it should be recalled that the holders of the right of self-determination are ‘all peoples’ without exception, and that the principle of territorial integrity can only be invoked in the case of external interference by another state and not as a pretext to restrict said fundamental right.

“The validity of the right of self-determination established by the Spanish constitution must prevail over the norms or resolutions of lower rank.”

However, international legal backing for a referendum appeared to cause some panic in the Moncloa, the Spanish equivalent of Downing Street. In interviews, three ministers from new socialist Prime Minister Pedro Sánchez’s government dismissed the idea.

Meritxell Batet, whose brief is the territorial administrations, told El Periódico: “It is not a matter of breaking a vote, but of finding a consensus solution in which an immense majority of society feels identified.”

Vice President Carmen Calvo told El País: “The referendum does not enter into any agenda of the government of Spain ... We are also the government of Catalans, both of the independentists and those who expect their government to live up to the peace they need.” Development minister, José Luis Ábalos, told daily newspaper ABC: “There is nothing to negotiate.”

Meanwhile, the lawyer for two of the deposed Catalan ministers who are locked up in Estremera prison – Oriol Junqueras and Raül Romeva – has said he has pressed charges against the man responsible for recording and leaking a video of his clients and a third inmate, sacked minister Joaquim Forn.

Andreu Van den Eynde said on Twitter: “We know who it is. We’re pressing charges immediately.”

The video emerged last week on the website of Catalan newspaper Ara and on television, and was condemned by the men’s families.

Reports suggest the video was filmed by a low-security inmate who befriended Junqueras and Forn.

El Periódico has named the man and suggested that he used a spy watch and was able to leave the prison to download material because of his low security status. He has not returned to prison for a week.