Vauxhall has revealed it first recorded a Zafira car bursting into flames due to a problem with its heating and ventilation system in 2009, several years before owners were contacted over the issue.
Campaigners claim more than 300 Zafiras have caught fire in recent years, leaving their occupants with just a few seconds to escape without harm.
In December, Vauxall wrote to all 234,938 Vauxhall Zafira B owners as it launched the first of two recalls in a bid to fix the problem.
Peter Hope, director of customer experience and corporate strategy at Vauxhall, told the Commons' Transport Select Committee that it first recorded a case of a Zafira suspected of catching fire over the issue in February 2009.
Asked by committee chair Louise Ellman why Vauxhall waited until 2014 before a full investigation was carried out, Mr Hope said: "Often when fires are reported (the cause is) not clear - either because the vehicles themselves are totally destroyed or because we don't have access to the vehicle to inspect it .
"For those vehicles prior to 2014, we didn't have enough evidence from the reporting system that we had to identify this as an issue that we could take action with.
"From 2014 onwards, there was a recognition of a pattern and that was then investigated extensively with our engineers."
Committee member Stewart Malcolm McDonald told the Vauxhall director: "This isn't good enough. You knew the car wasn't safe and you sat on your hands for so long."
The SNP MP described the company's response as "wholly inadequate", and - citing the Volkswagen diesel emissions scandal - asked Mr Hope why the car industry "seems to treat its customers with complete contempt".
In his response, Mr Hope said: "There are always areas of any manufacturer's actions where you think 'I would have loved to have either known that earlier or taken action earlier'.
"But we didn't at that stage. Is that acceptable, is that something I feel happy with? No.
"But what I'm really trying to assure you is that it is never about casualness or contempt or a lack of taking this seriously. That is not the way we think."
Figures released in May by London Fire Brigade (LFB) show it has attended 120 Zafira fires since 2013, including 14 this year.
Vauxhall launched a first recall of the cars in December to correct the issue, which it said was caused by improper repairs to the people carrier's blower motor resistor.
Described by the car maker as "preventative action", the second recall - announced in May - will involve "improving the overall robustness of the system" as opposed to simply replacing the resistor and its fuse, which the firm started doing last year.