A probe into the management of the global banking and markets (GBM) business at the institution was started by the Financial Services Authority (FSA) in April 2009.
The investigation is thought to have focussed on âconduct, systems and controlsâ within the unit.
Mr Cameron oversaw the department which led to the acquisition of Dutch bank ABN Amro in 2007 - a move viewed as being partly responsible for the near-collapse of RBS during the global credit crisis.
The industry regulator is thought to be close to unveiling a settlement with the ex-RBS banker who, although not being accused of any illegal behaviour, will be the most senior executive from the institution to be penalised.
He is reported to have begun work with Odgers Berndtson as an advisor but resigned from the post after the firm lost a mandate from the UK Financial Investments.
Meanwhile, a pair of ex-bankers from Northern Rock received penalties from the FSA.
David Baker, former deputy chief executive of Northern Rock and Richard Barclay, former managing credit director at NR, were issued fines of Â£504,000 and Â£140,000 respectively during April.
By Jim Ottewill