A British Labour MEP of 20 years has told of an orchestrated attempt to hound him out of a key role in the European parliament on the basis of his nationality.

Claude Moraes claims to have had his position systematically attacked, with the encouragement of Spain, after blocking EU “no deal” legislation that proposed to describe Gibraltar as a colony in a footnote.

Senior Spanish MEPs have been seeking to push Moraes out of his role as the chamber’s rapporteur, a role in which his job is to represent MEPs’ views on draft legislation.

The row culminated on Tuesday morning with the MEP being asked to step down by the European parliament’s speaker, Antonio Tajani.

“And I told him: no,” Moraes said. “The inclusion of this footnote on Gibraltar was a political act which is now being defended by 27 member states and the commission in an unprecedented way.”

The MEP said his own vulnerability showed how the UK’s weakness would be exploited by the EU in the years to come.

“For five weeks the pressure has been systematic,” Moraes added. “The attacks in the Spanish press have been very brutal, very personal, and consistently so. There has been pressure by all the political groups in the European parliament with Spanish members. There have been meetings where I have been attacked systematically – it has been an intimidatory atmosphere.”

Moraes has repeatedly refused requests during five so-called “trilogue negotiations” with the European commission and the council of the EU, representing the member states, to sign off legislation putting the UK on a list of countries whose nationals need not apply for a visa to travel to the bloc in the event of a no-deal Brexit.

The veteran MEP said he did not have any mandate from his civil liberties committee to agree to the inclusion of a description of the British overseas territory of Gibraltar as a colony, a term pushed by Madrid and agreed by the other 26 member states.

But, last week, on the instigation of Spanish MEP Esteban González Pons, the centre-right European People’s party, the Socialists and the liberal ALDE group demanded action by Tajani over Moraes’ “conflict of interest” as a British national.

Tajani formally asked Moraes to stand down on Tuesday morning. The MEP’s subsequent refusal means the parliament’s president is likely to seek a way to force him out of the role.

Moraes said he had no doubt that Spain was behind the attempt to unseat him or that it was linked to the coming general election in which the socialist government is seeking to minimise the damage from the growing populist party, Vox.

Last month the Spanish foreign minister, Josep Borrell, said the hold-up on the visa legislation was “one of the problems of having the British with a foot in and a foot out” of the EU. Spanish sources have suggested it is irresponsible for Moraes to continue to block the legislation which would affect millions of people.

Moraes said: “I have kept on because there have been very many members who have been supportive, who realise that this is a political situation, with an election in Spain.

“But my position is that if the European parliament submits to this sort of behaviour when there is a national election on, the whole raison d’être of the European parliament is removed. Legislation is supposed to be made on the basis of the legislation.

“This was contingency legislation without a political element. But there has been an opportunistic line taken which has put me in an impossible position. It is an abuse of power.”

Moraes said the committee of civil liberties had voted by 53-0, including two Spanish MEPs, in favour of the legislation when it had not included the contentious footnote.

The Labour MEP added that he had proposed various compromise footnotes over the past five weeks referring to the continuing dispute over the sovereignty of Gibraltar but they had all been dismissed out of hand.

“But this goes to the heart of the status of Gibraltar internationally,” Moraes said. “Gibraltar had a referendum on self-determination. It has a complex but clear position as part of the UK.

“It is not a colony. If it was described as a colony, Spain would be able to start making claims in international law, and that is why they wanted this definition. And the people of Gibraltar were extremely alarmed because once it is used in this context it will be used again and again.”

If the UK is not on the visa-free travel list, or on a list of countries whose residents require a £52 visa, British citizens will be left in legal limbo.