A Southampton taxi firm boss says he will seek a judicial review to overturn a rule which requires cameras to be installed in all city cabs.
On Thursday a judge ruled in favour of the council, saying the rule was a policy which he had no jurisdiction over.
However, he said that, if he had been able to, he would have ruled in favour of Radio Taxis director Kevin May.
The council has said cameras were needed for safety reasons.
It introduced the licensing condition two years ago and all taxis and private hire vehicle are now required to have a CCTV camera which records images and all conversations in the cabs.
Mr May said it was an invasion of privacy, as the cameras could not be switched off even when drivers were using their cars for private reasons.
He said cameras which the drivers could activate if they felt threatened, while at the same time warning their passengers they were doing so, would be more acceptable.
Recorder Stewart Patterson, sitting at Salisbury Crown Court, said if he had had the power to rule in the case, he would have found the camera use was "not lawful and was not justified".
He said recording conversations and images while the vehicle was in private use was "invasive", "disproportionate" and a "violation" of Article Eight of the Human Rights Act, the right to privacy.
In his judgement, he said: "If the policy were to be amended and the condition limited to visual recordings while the vehicle was in operation as a taxi, the policy would in our view be justified... and therefore lawful."
Mr May, who has spent £30,000 of his own money fighting the rule, said the policy had left some drivers unable to work because they could not afford to have the cameras installed or repaired.
He said: "[The judge] knows the situation I'm in and he's looked at what the council are doing and says they shouldn't be doing it.
"Because the judge has deemed the policy unlawful, I think it opens up the door for a judicial review.
"If the council decides to do nothing about this, we will go down that route. We'll fight it all the way."
Councillor Royston Smith, leader of Southampton City Council, said the judgement was "a victory for the safety of drivers and passengers in taxis in the city and wider country".