The current British definition of terrorism is so broadly drawn that it could even catch political journalists and bloggers who publish material that the authorities consider dangerous to public safety, said the official counter-terrorism watchdog.

David Anderson QC, the official reviewer of counter-terrorism laws, said Britain had some of the most extensive anti-terrorism laws in the western world, which gave police and prosecutors the powers they needed to tackle al-Qaida-inspired terrorists, rightwing extremists and dissident Northern Irish groups.

"But if these exceptional powers are to command public consent, it is important they need to be confined to their proper purpose, and recent years have seen a degree of 'creep' in parliament that could be reversed without diminishing their impact"

In his annual report to be published on Tuesday, Anderson is expected to give three examples of how the terror laws were too widely drawn.

They included "actions aimed at influencing governments", hate crime and what he called the "penumbra of terrorism".

On the first, Anderson said Britain's laws treated politically motivated publication of material thought to endanger life or to create a serious risk to the health or safety of the public as a terrorist act if it was done for the purpose of influencing the government.

He said in other European and Commonwealth countries the bar was set much higher and there must also be an "intention to coerce or intimidate".

The watchdog said: "This means political journalists and bloggers are subject to the full range of anti-terrorism powers if they threaten to publish, prepare to publish something that the authorities think may be dangerous to life, public health or public safety."

He warned that they could be branded as terrorists even if they had no intention to spread fear or intimidate, and those who employed or supported them would also qualify as terrorists.

The definition was so broad it would even catch a campaigner who voiced religious objections to a vaccination campaign on the grounds that they were a danger to public health.

On hate crimes, Anderson said the law made a terrorist out of a pupil who threatened to shoot their teacher on a fascist website, or of the racist who throws a pipe bond at their neighbour's walls. Both were obvious criminals, but if they only intended to harm their immediate victims, no purpose would be served by branding them as terrorists, Anderson said.

The laws were so widely drawn that they now included preparatory and ancillary offences including "terrorism-related activity", which were only used when a crime had been committed and so were unnecessary.

These definitions were so "overbroad" that they could catch a family member "who supports someone who encourages someone else to prepare an act of terrorism and could easily be limited by the home secretary", the watchdog said.

Anderson said Britain quite rightly had very tough counter-terror laws that the public accepted so long as they were used only when necessary.

"But they can currently be applied to journalists and bloggers, to criminals who have no concern other than their immediate victim, and to those who are connected with terrorism only at several removes," he said.

"This is not a criticism of ministers, prosecutors or police – who as a rule exercise either their remarkably broad discretions with care and restraint. But it is time parliament reviewed the definition of terrorism to avoid the potential for abuse and to cement public support for special powers that are unfortunately likely to be needed for the foreseeable future."