Lord Camoys, a Roman Catholic descendant of Charles II and former Lord Chamberlain to the Queen, worked there between 1991 and 2006 and is thought to have called out the Vatican more than once over fears about money misuse.
According to The Times he came across some 'grey-area' banking deals.
11 years ago Lord Camoys is thought to have written a detailed letter to Vatican officials in which he raised his concerns over the Vatican's banking and warmed of a "very serious risk of becoming involved in money laundering."
He also disclosed that he did not feel the Vatican even needed a bank.
Speaking after the election of Pope Francis in 2013 he said: "I mentioned some of these concerns, but perhaps I did not explain myself clearly enough."
His letter was revealed this week by Italian journalist Gianluigi Nuzzi in his book Merchants in the Temple.
It used leaked documents to allege the misuse of funds and corruption in the Vatican.
The Times has also reported that in 2013 the Pope oversaw the closure of a suspicious account and once again a letter was sent by Nigel Baker, the British ambassador to the Vatican, backed up by Lord Camoys.
Mr Nuzzi wrote about this incident in his book: "The document was interpreted by the men closed to Francis as further proof that many at the Apostolic See knew how critical things were but had no intention of changing their approach."
The book also alludes that the Vatican was in talks with a tobacco company for promotional campaigns.
