Dozens of defendants are due to go on trial at the Brazilian Supreme Court on Thursday in what is billed as one of the biggest political corruption scandals in the country’s recent history.

The case will be closely watched by the governing Workers’ Party (PT) and former President Luiz Inacio Lula da Silva, who remains a key figure in Brazilian politics.

The judges will consider allegations that, between 2003 and 2005, politicians and officials diverted public funds to buy political support for Lula’s government. The scheme became known as “mensalao” or the “big monthly” allowance.

BBC Brasil explains the background.