The Competition Commission has said it has yet to reach firm conclusions about its investigation into payment protection insurance (PPI).
PPI has come in for criticism from consumer bodies
It has found evidence that the cost of PPI can be greater than the interest paid on loans.
But it says the issues under consideration are "by no means simple", and has invited further evidence from interested parties.
Provisional findings are expected to be published in May 2008.
In a document setting out the Competition Commission's "emerging thinking", inquiry chairman Peter Davis said that after examining a "substantial" amount of evidence, he believed that there were some areas that required further exploration.
"We are far from making up our minds," he added, "but we are focussing on the amount of competition for PPI that distributors face at the retail level."
PPI covers repayments on loans, mortgages and credit cards if the borrower is unable to make them because of loss of earnings as a result of accident, sickness, unemployment or death.
It has been widely criticised by consumer groups for being expensive and offering limited benefits to policyholders.
Earlier this year the consumer organisation Which? argued some people were "tricked" into buying PPI because many lenders automatically include the cost of the insurance in a loan quote.
The Office of Fair Trading referred the £5bn market to the Competition Commission in February, after a "super-complaint" from Citizens Advice prompted it to carry out its own year-long investigation.
Despite agreeing that PPI could provide "worthwhile cover" for some consumers, the OFT highlighted several market failings.
It concluded that consumers do not shop around for the best deal, partly because the complex nature of the product makes comparison between different policies difficult.
The Competition Commission acknowledges that consumers face an important decision when choosing whether or not to take out PPI as they try to balance the benefits against the cost.
It says it has evidence that in some instances the insurance policy is more expensive than the interest paid on the loan itself.
Inquiry chairman Peter Davis said he was "well aware of the concerns surrounding PPI, "and that the inquiry team aimed to conclude its work "as speedily as possible".
But, he added, "we are also conscious that the issues we are deciding upon are by no means simple and it is vital that we carry out our work thoroughly, ensuring that all parties receive a fair hearing."
GE Capital Bank £610,000
Redcats (Brands) Ltd: £270,000
Capital One Bank £175,000
Regency Mortgage Corp: £56,000
Home & County Mortgages: £52,500
Capital Mortgage Connections: £17,500
The Competition Commission is therefore inviting comments on the views expressed in its "emerging thinking" document, and nine separate working papers on different aspects of PPI.
The deadline for responses is 27 November 2007, and the inquiry team expects to publish its provisional findings in May 2008.
Mr Davis added that the Competition Commission was working closely with the City regulator, the Financial Services Authority, which has taken enforcement action against 10 firms over concerns about the sale of PPI.
It has fined eight firms a total of £1.8m and publicly censured two others. It also ordered the firms to review more than 1.5 million policies and, where appropriate, to offer redress.
In addition the FSA has announced it will publish tables which will let consumers compare various PPI policies on its consumer website in March next year.