George Bush finally broke his self-imposed vow of silence on Barack Obama to attack him over the recession, health reform and Guantánamo.

In a speech to a business convention, Bush repeated several times the mantra that he would not criticise his successor before going on to do just that, the first time since leaving office on 20 January.

The former president, in an hourlong appearance in which he made a speech and took questions, argued healthcare should be left to private insurance companies.

"There are a lot of ways to remedy the situation without nationalising healthcare," Bush said. "I worry about encouraging the government to replace the private sector when it comes to providing insurance for healthcare."

Obama is hoping to have legislation in place by October that will offer a federal insurance policy to rival private insurance.

The former president, though he did not directly name Obama, also rounded on his $775bn (£473bn) stimulus package, arguing that businesses were better placed to make judgments about spending than the White House.

"I know it's going to be the private sector that leads this country out of the current economic times we're in," he said. "You can spend your money better than the government can spend your money."

The speech, in Erie, Pennsylvania last night, was only his fourth since leaving office in January, two of which were in Canada.

Bush's silence until now was one of the reasons why his vice-president Dick Cheney has been giving interviews and speeches, defending the Bush administration record and criticising Obama, particularly the controversy over the interrogation techniques used at Guantánamo and CIA detention centres round the world.

Obama described the techniques approved by the Bush administration as torture and disputed that they produced valuable intelligence. But Bush yesterday said he had decided to "use every technique and tool within the law to bring terrorists to justice before they strike".

Bush also took a swipe at Obama over his planned closure of Guantánamo. "I told you I'm not going to criticise my successor," he said.

"I'll just tell you that there are people at Gitmo that will kill American people at a drop of a hat and I don't believe that - persuasion isn't going to work. Therapy isn't going to cause terrorists to change their mind."