The Trident whistleblower, William McNeilly, has accused the Ministry of Defence (MoD) of trying to "brainwash" the public into believing that nuclear weapons are safe.

In a new message to the public, he says that people are being deceived about the security of Trident nuclear warheads carried by submarines based at Faslane and Coulport on the Clyde. A terrorist attack is highly likely, he claims.

McNeilly disclosed last week that he had been dishonourably discharged by the Royal Navy for making public a dossier alleging that Trident was "a disaster waiting to happen" and going absent without leave. He is promising to say more in July.

The Sunday Herald revealed his allegations on May 17, while he was on the run. The following day he handed himself in to police at Edinburgh airport, saying he had achieved what he wanted.

His dossier, which detailed 30 safety and security flaws on Trident submarines, was raised in the House of Commons by the former SNP leader, Alex Salmond. But it was dismissed by the MoD as "factually incorrect or the result of misunderstanding or partial understanding".

McNeilly, a 25-year-old naval recruit from Belfast, was on patrol with the Trident submarine, HMS Victorious, from January to April this year. He posted a new report online last week defending the accuracy of his allegations.

"All of the charges against me were dropped," he said. "It's only a matter of time before worse information comes out, and everything is proven to be true."

He then posted another message on Facebook "for those brainwashed people who believe everything the military tell them." He referred to the false claim in the run-up to war that Iraq had weapons of mass destruction.

"You were lied to about nuclear weapons in Iraq, and now you're being lied to about how safe and secure the weapons are on your homeland," he said.

"The government overestimated Saddam and now they are underestimating the Islamic State. If things stay the way they are I put the odds of a terrorist attack at some point in the next eight years at around 99 per cent."

He claimed that his concerns about lax security at Faslane had been backed by senior military figures. "The equipment that is brought on board by civilian contractors and military personnel isn't checked," he said.

"People are in positions without the proper security clearance. Mass amounts of people are being pushed through the system due to manpower shortages. IDs aren't being checked properly."

A pin code at a security gate wasn't being used "because it's either broke or people just get buzzed through because they've forgotten their pin," he said. "It's ridiculous."

It was wrong to regard current security as "the best we can do" when it wasn't, he argued. "It's literally harder to get to the careers office in Northern Ireland than it is to get down a nuclear submarine."

People have become far too relaxed in the war on terror, he claimed. "The fact is anyone with a couple of fake IDs can get unto a nuclear submarine," he added. "Islamic State have already shown that they can acquire fake documentation and IDs."

McNeilly called for security to be tightened, and for the removal of Trident missiles. "The military seem to be happy with the security at the site," he told the Sunday Herald.

"Islamic State have the ability to easily penetrate through the security that the navy is currently providing. The site's security must be heightened above its current highest state until the missiles are removed."

In his Facebook post he also revealed that he had been accused of working for the anti-nuclear movement. "Some think that I'm a spy for the SNP or CND: that's ridiculous," he said. "Just because they also have a desire to protect the public from Trident doesn't mean that I'm working for them."

He claimed that other nuclear submariners were afraid to speak out. "They are given money, taken to a dark place away from the public, put in unnecessary danger and basically told 'don't tell anyone what happens here or we'll both get in trouble'.

McNeilly's stance was welcomed by most of his Facebook friends. "I think what you have done is patriotic to the human race," said Steven Baker.

"Well said and full credit to you, mate," wrote Paul Hepburn. "What you did took an enormous amount of courage. Well done."

Darren John Kerr added: "As a veteran myself, I fully support you. If the public only knew what the services got up too."

A few were critical, though. "You're not worthy of having ever been associated with the Royal Navy," wrote Sarah Lou. "You're an idiot," said Del Walker.

The MoD referred the Sunday Herald to earlier comments it had made in response to McNeilly's allegations. It initially described his claims as "subjective and unsubstantiated" and said it disagreed with them.

In a statement to the House of Commons on May 28 the Defence Secretary, Michael Fallon, denied that safety had been compromised. "Most of McNeilly's concerns proved to be either factually incorrect or the result of misunderstanding or partial understanding," he said. "Some drew on historic, previously known, events, none of which had compromised our deterrent capability."

Last week an MoD spokeswoman confirmed that McNeilly had left the Royal Navy. "Throughout the process he was afforded the duty of care that we give all our personnel, as was his family," she said.

According to the MoD, the future employment of individuals had to be considered when they showed a willingness to breach trust, ignored opportunities to voice concerns through the chain of command and declared "beliefs incompatible with service employment".