Taxi company Uber has been at the center of controversy having unleashed its wave of self-driving Volvo XC90s onto the streets of San Francisco last week. There were safety concerns, unsurprisingly, which wasn't helped by a video that emerged showing a self-driving Uber failing to stop for a red light on the day the service launched. Then it was revealed that Uber didn't seek any permits to test the technology, prompting state regulators to order the firm to shut the scheme down and seek a permit, or face legal action.

Mayor Ed Lee ordered the firm "to stop the unpermitted and unlawful testing of autonomous vehicles." Given its history of rebelling against government guidelines, it comes as no surprise that Uber is remaining defiant and will continue to test its self-driving taxis despite threats of legal action. "We respectfully disagree with the California DMV's legal interpretation of today's automation regulations, in particular that Uber needs a testing permit to operate its self-driving cars in San Francisco," Anthony Levandowski, who leads Uber's automation efforts, said in a statement.

He argues that a permit isn't required because someone is still sat behind the wheel, meaning that the car is not fully autonomous and is similar to Tesla's autopilot technology. "We believe Tesla is right and our vehicles are just like Tesla's. The vehicle is not capable of driving without a human operator. As long as that's the case, it's not an autonomous vehicle," he concluded. The difference, however, is that Tesla requires the driver's hands to be on the wheel. A warning is issued if their hands are off the wheel and the car will gradually slow down. This is not the case in Uber's cars, as drivers can hover their hands a few inches away from the wheel without any interference, so his argument doesn't completely stand up.

As for the Uber that jumped the red light soon after the scheme started, the firm is blaming the person behind the wheel, who has apparently been suspended. Wired reports that the situation has been escalated to the attorney general to try and enforce legal action, but it isn't clear what the outcome will be. "The Mayor is working with the DMV, state officials and the city attorney's office to explore all possible avenues available to us to enforce state law," a statement from the mayor's office said.

Whether Uber has a strong case remains to be seen, but a letter sent to the company by the attorney is threatening a court-ordered ban if Uber ignores the request. Which you can guarantee it will. Where do you stand on this autonomous car debate?