A top politician who was filmed by police at a Brighton demonstration wants to ban the authorities from keeping pictures of law-abiding protesters.

Sue Miller, Liberal Democrat home affairs spokeswoman in the House of Lords, told The Argus she would be pushing for a change in the law when Parliament returns in October to prevent innocent people being “treated as criminals”.

The peer, who warned of the risk of the UK becoming a “police state”, said her campaign had been prompted by her own experiences at a peaceful protest in Brighton, which she attended while visiting friends in the city.

The rally, outside Brighton Town Hall in December 2007, was organised to protest against Sussex Police’s use of council by-laws on noise control to curtail demonstrations against Moulsecoomb-based arms manufacturer EDO MBM.

Baroness Miller, who recalls between 20 and 30 protesters showing up and singing “a couple of songs”, said about five or six police officers attended and one filmed “the whole thing”.

When she asked one of the officers why they were being filmed, she was told it was “in case something criminal happens later”.

The peer told The Argus: “I was just another protester and I found the police’s attitude pretty hostile.

We just stood outside the council building and sang a couple of songs.

You can’t get much more peaceful than that.

I couldn’t imagine why they needed to film us and I’m sure my picture is still on record.”

She said: “I am questioning the idea that protesters should be treated as criminals when they are doing nothing wrong.”

Noting last December’s ruling by the European Court of Human Rights against the indefinite retention of innocent people’s DNA on the national police database, and subsequent Government concessions, Baroness Miller said: “Unless you have committed a crime they shouldn’t be holding information on you.

Photos are as personal as DNA.

I do not believe that images of innocent people should be kept on any sort of database.

“The country has gone so far into surveillance and keeping records on citizens when there is no reason to.

“Once they start along this route it is such a short move to a police state.”

Baroness Miller said she planned to propose amendments to the Coroners and Justice Bill when it returned to the Lords for its Report Stage in October to outlaw retention of such images by police.

She also plans to ask Sussex Police whether it still holds any images of her on its files.

It is not the first time Sussex Police has been criticised over surveillance.

In February, Brighton Pavilion MP David Lepper accused the force of “intimidation” after its officers appeared to photograph people entering and exiting the Cowley Club in London Road, Brighton, for a meeting.

In a separate incident, John Catt and his daughter Linda complained they were the victims of a police state after a marker was placed against their car on the Police National Computer because they had attended three protests against EDO MBM.

A camera in central London that automatically recognises number plates flagged them up and they were pulled over and searched by a police anti-terrorism unit.

Sussex Police has said photography at protests is part of ongoing police work to gather information to support future operations.