If you approach the St Anna’s gate entrance to the Vatican and look to your left, past the Swiss Guards on duty, you will see a large, round medieval edifice.

This fortress-like building is the tower of Niccolò V, named after a fifteenth-century renaissance pope renowned for his passion for construction. Today, the tower is home to the Institute for the Works of Religion (IOR) – better known as the Vatican Bank.

For years it has been embroiled in scandal. In the 1970s and 1980s the IOR was caught up in the collapse of two Italian banks. Last year Vatican accountant Mgr Nunzio Scarano – dubbed “Mgr Cinquecento” for his liberal use of €500 notes – was put on trial for allegedly trying to smuggle €20 million in cash from Switzerland to Italy. He was cleared of the charges but found guilty of making false accusations against a co-defendant. Such was the concern about the Vatican’s failure to abide by anti-money laundering rules that in January 2013 Italy’s central bank blocked all electronic payments through cash machines and credit cards in Vatican City State.

Two months later Pope Francis brought in the formidable Australian Cardinal George Pell to overhaul the bank’s leadership and put in place new money-management controls. In spite of fierce resistance – Pell’s plan for auditors PricewaterhouseCoopers to go through all the books was blocked – much has been achieved during his four years in office. Meanwhile, the word in Rome is that the Vatican’s real financial powerhouse, APSA (Administration of the Patrimony of the Holy See) – which manages properties and investments – is reluctant to submit to independent scrutiny. Mgr Scarano used to work for APSA.