The FSA has rejected calls to provide details of the remit given to the research consultancy investigating commission transparency.
Brokers had voiced their concern over the nature of the questions posed by the consultancy, CRA International.
They claimed the questions were skewed in favour of mandatory commission disclosure, prompting calls for the FSA to disclose the remit given to CRA.
"The questions give the clear impression that the FSA is determined to introduce commission disclosure, driven by a desire to stamp out profit shares and overriders," said one broking source.
But the FSA refused to provide details of the full remit given to CRA. In a statement it said: "The independent consultants will gather detailed and balanced evidence of the extent to which a lack of transparency is disadvantaging commercial customers, and whether mandating commission disclosure will lead to benefits to the market that outweigh the costs of introducing it."
CRA is currently interviewing wholesale brokers, clients and insurers.
The FSA said the first stage of CRA's work would look at whether there were any substantive market failures associated with a lack of commission transparency.
The second stage of the review will estimate the likely costs and benefits of compliance if mandatory commission disclosure is introduced.
"This cost benefit analysis will be based on further interviews and survey responses from firms," said the FSA.