As a result, the group said, matters will become "very complicated" for the government if it seeks to maintain its existing authorisation for the drilling off what is known as the Vicentine coast, much of which is protected.

"We know that up until today there have been thousands of written submissions from people who expressed an opinion against the awarding of this title of private use of maritime space," Zero's president, Francisco Ferreira, told Lusa.

The group is "very keen [to know] what the government will say in view of what is an enormous majority of negative opinions, duly substantiated, that the exploratory drilling should not go ahead," Ferreira said.

"I think it will be a very complicated option if the government, in view of all the opposition and argumentation made under the awarding of this title, goes and considers it has valid," the Zero president said, adding that this was independent of the fact that the consortium in question has already said publicly that it will not press ahead with drilling for now.

The public consultation on exploratory drilling of a first well by the consortium led by Italy's ENI, and of which Portugal's Galp Energia is a member, some 46.5 kilometres offshore in the area of Aljezur, in the Algarve, ends on Wednesday, after the government decided to extend the period for an extra 30 working days. The deadline was initially 21 June.

According to Ferreira, among the problems are the lack of information from studies for citizens and organisations to be able to form an opinion and give arguments for their submissions. Although matters improved slightly after the extension of the deadline, with studies being posted online, this was still "short of what would for us be crucial," he said.

Among the missing data were "studies relative to the modelling of an accident that really does have a very low probability, but which could happen, as well as an assessment [of] this risk ... in terms of impact on eco-systems ][and] for health."