BRASILIA - Brazil's ex-president Luiz Inacio Lula da Silva continues to hold a significant lead in pre-presidential election polls, despite being behind bars, according to a survey released on Tuesday.

Polling firm Vox Populi said the leftist Workers' Party (PT) leader, who planned to run for reelection until top courts declined his appeals and ordered him to begin serving his 12-year sentence on corruption charges, would likely win in the first round, if allowed to compete.

The survey carried out between April 11 and 15 at the request of the PT, shows Lula enjoys substantial 47 percent support among the electorate, versus 12 percent for the next closest candidate, the arch-conservative Jair Bolsonaro.

Lula's chances of participating in the October elections appear dim, especially due to Brazil's Clean Record Law, which bars politicians with convictions from running for office for a period of eight years.

However, it cannot be ruled out either, since Brazil's legal system provides a range of reprieves and other recourse.

The survey also shows most Brazilians believe Lula should not have been convicted for allegedly accepting perks from a construction company in exchange for juicy government contracts, including the use of a luxury beachfront apartment.

Lula has maintained his innocence throughout, and claims the accusations and trail were politically motivated to derail his presidential run.

Some 41 percent of those surveyed said Lula was convicted without proof; 44 percent believe he has been unjustly imprisoned; and 58 percent think he has the right to run again, possibly once he completes his sentence.

However, chances are this would be his last opportunity as the popular elder statesman is 72 years old.

The head of Vox Populi, Marcos Coimbra, said the poll shows public sentiment for Lula has grown, with many seeing him as a victim of a biased judicial system.

A similar survey released on Sunday by pollster Datafolha also showed Lula in the lead, but by a slimmer margin of 31 percent, with Bolsonaro trailing with 15 percent.