It reads like a racy political thriller. Lina Vieira, the recently fired head of Brazil’s revenue service, claims that while in office she was summoned to a secret meeting with Dilma Rousseff, the government’s senior minister, and asked to “speed up” an investigation into companies owned by the family of José Sarney, president of the Senate.

Ms Vieira says this was a request for a whitewash. Ms Rousseff – expected to run for president next year as the chosen successor to Luiz Inácio Lula da Silva – denies requesting any such thing and says the alleged meeting never took place. Ms Vieira is due to give evidence on the affair on Tuesday to a Senate committee. Were she to prove that the minister lied, some analysts say, Ms Rousseff’s political career would be over.