An 86-year-old man has been granted permission to launch a lawsuit against police chiefs who have classified him as a "domestic extremist" and kept a detailed record of his political activities on a clandestine database.

John Catt, who has no criminal record, is bringing the high court action against a secretive police unit which systematically logged his presence at more than 55 peace and human rights protests over a four-year period.

Some of the entries record his habit of taking out his sketch pad and drawing the scene at demonstrations. Other entries contain notes on his appearance – such as "clean shaven" – and the slogans on his clothes.

His lawsuit will challenge the power of police to compile secret files on law-abiding protesters.

A victory for Catt, a pensioner who lives in Brighton, would be a further blow to the police unit, which has been criticised for using undercover officers to infiltrate protest groups.

The exposure of spies such as Mark Kennedy, who spent seven years working undercover in the environmental movement, has highlighted the way in which the National Public Order Intelligence Unit has been carrying out surveillance of protesters.

The unit has been compiling a huge, nationwide database of thousands of protesters for more than a decade, drawing on intelligence from undercover officers, uniformed surveillance teams, informants in protest groups and covert intercepts.

Police claim the unit only monitors so-called "domestic extremists", whom they define as hardcore activists who commit crime to further their political aims.

Catt, a campaigner for many years, is one of the few activists confirmed to be on the database.

He says he is "committed to protesting through entirely peaceful means" and told the Guardian he was "shocked and terrified" after he saw the extent of the files held on him. He obtained them using the Data Protection Act.

In legal papers, he describes how the files record the political aims of the demonstrations he attended between 2005 and 2009, "highly personalised" information about his appearance and "hearsay evidence and police officers' opinions".

Peace activists John and Linda Catt tell their own story of being monitored by police and placed on a secret database of 'domestic extremists' guardian.co.uk

At a protest against Guantánamo Bay organised by Sussex Action for Peace on 25 September 2005, police noted: "John CATT was seen wearing a Free Omar T-shirt, he was clean shaven … John CATT was very quiet and was holding a board with orange people on it."

At another protest on 10 March 2006, police recorded: "John CATT arrived in his white Citroën Berlingo van. He removed several banners for the protesters to use and at the completion of the demo returned the same to the van. He was using his drawing pad to sketch a picture of the protest and the police presence."

On another occasion he was logged as having "sat on a folding chair and appeared to be sketching" at a demonstration.

Police tracked his van after noticing it at demonstrations. He and his daughter Linda were stopped and searched one Sunday morning in London by police who were alerted by a roadside camera recognising the van's number plate. The pair had been on their way to help a family member move house.

Catt, who is represented by the London law firm Fisher Meredith, has been given permission by a high court judge to take legal action against police chiefs, as he claims they have violated his human rights by keeping "excessive and irrelevant" secret files on him.

He wants all the entries concerning him to be permanently deleted.

Police chiefs say they are legally entitled to maintain files on Catt, who has been taking part in a campaign to close down a Brighton arms factory owned by an American firm, EDO MBM Technology. According to police, the Smash EDO group has organised a "campaign of illegality designed to pressurise EDO to cease its lawful business", leading to "169 convictions including criminal damage and aggravated trespass, assault and harassment of staff".

The "minor" surveillance of Catt is justified, they say, because his "voluntary association at the Smash EDO protests forms part of a far wider picture of information which it is necessary for the police to continue to monitor in order to plan to maintain the peace, minimise the risks of criminal offending and adequately to detect and prosecute offenders".