The Co-op has been ordered by a watchdog to give clearer information to drivers about their insurance costs.
An order that came into force in August last year obliges private motor insurance providers to present customers with information on the costs and benefits of no claims bonus protection, as part of moves to boost competition and reduce drivers' premiums.
But the Co-op was the only one of the major insurers to miss the deadline, the Competition and Markets Authority (CMA) said.
Based on figures provided by the Co-op, the CMA said an estimated 90,000 new business quotes and 30,000 renewals have been affected since August, when compliance with the order was supposed to have been achieved.
The CMA said from February 1, the Co-op's prospective new customers will be given two quotes, one including no claims bonus protection and one without, so that they can calculate the actual price of the protection. Customers will also be given the option of telephoning the company in order to get the information.
In addition, Co-op Insurance has been ordered to ensure that, by no later than October 1, all customers must be able to see the price they will be charged on the company's website and in written offers and documents.
Adam Land, senior director of remedies, business and financial analysis at the CMA, said: "It is very disappointing that a major company such as Co-op Insurance has taken so long to provide this vital information to its customers.
"Before the order came into force, the price and benefits of NCB (no claims bonus) protection were often unclear to drivers.
"We expect the Co-op to fully comply with the terms of our directions immediately so that motorists can search more easily for the best deal for them and decide whether or not they want this optional cover."
A spokeswoman at the Co-op Insurance said: "For 90% of our new business customers, we are already fully compliant with this order. We are part way through a major transformation programme, which when complete will allow us to be fully compliant and enable us to provide best in class service to our members.
"We continue to keep the CMA aware of our progress and have been working collaboratively with them on interim solutions. We are working to be fully compliant by the agreed date of 1 October 2017."