Police have sent hundreds of letters to anti-cuts activists warning them of the consequences of attending a 10,000-strong student demonstration in central London on Wednesday.

The letters have been sent to anyone arrested in connection with previous public disorder offences even if they were later cleared or charges were dropped.

The police have admitted the names and addresses come from a database of those arrested during anti-austerity protests. They include protesters aged 17.

At a briefing on Monday, Metropolitan police officials said letters would only be sent to those who had been convicted of offences. But on Tuesday the force confirmed that anyone who had been arrested in the past year in relation to an "austerity related" protest had been sent the warning.

The letter, which arrived on Tuesday, reads: "It is in the public and your own interest that you do not involve yourself in any type of criminal or antisocial behaviour. We have a responsibility to deliver a safe protest which protects residents, tourists, commuters, protesters and the wider community. Should you do so we will at the earliest opportunity arrest and place you before the court."

Signed by Simon Pountain, the Met commander leading Wednesday's operations, the letter goes on to warn of the detrimental effects of conviction on their chances of employment and says that if people find themselves near disorder they should move away at the earliest opportunity.

Pountain said the 450 letters had been sent to "those people that have been arrested at all the austerity measure related demonstrations over the last 12 months". This included student demonstrations, the 500,000-strong union-organised demo last March and those involved with industrial action on 30 June. Pountain said that selection "wasn't random"."This is about the police service doing our job and keeping those details," he said. "To be fair, the letter has gone to people that have been arrested at protests. If they didn't need warning then fine but actually a lot of people arrested in the past would perhaps to be reminded that it would not be a good thing to come along to seek to get involved in any problems. And that's our message.

"Some of those people might think, 'Do you know what, the police are right here: I won't go and I won't commit trouble'," he added.

Pountain denied the letters would have a chilling effect on protest and said the police service was "apolitical".

The warning letters come on the back of police briefings highlighting the force had sought authority to fire rubber and plastic bullets.

Pountain said police had no intention of deploying baton rounds but revealed officers had been given authorisation by the assistant commander to use rubber bullets during student protests last December.

"They won't be on show, they won't be on the street. But in the unlikely event of something very serious happening which would meet the criteria for use they are available for use," he said.

David Cameron said on Tuesday he would not criticise the police if they felt it was necessary operationally to use rubber bullets on the student demonstrators.

Essex sixth form student Tyler Perkin, who had charges dropped in relation to a peaceful UK Uncut protest at the Fortnum and Mason store in March, said he was horrified he was still on a police database.

"It's a disgusting attempt to try and scare us off from protesting," he said.

"It's also disgusting that we are all been kept on some database even though we haven't been charged … even though my case has been dropped they're still using it against us."

He said he had also been visited by police in conjunction with this summer's riots even though he had no connection with them.

Rhona Friedman, a lawyer, said, "The letter is being sent to young people who have not been convicted of any criminal offence but whose names must appear on the police intelligence data base of those engaged in protest.

"Whether deliberate or not the message is being received as being less about public protection and more about sending a chilling Big Brotheresque warning about the consequences of participation in public demonstrations."

Organisers of the march, which will set off after midday on Wednesday and join Occupy London Stock Exchange protesters who are camped around St Paul's Cathedral, have written to police warning them that children will be part of the demonstration after they learned of the authorisation of rubber bullets.

Baton rounds are regularly used in the UK. Since 2002 they have been used by police to stop fleeing vehicles or in cases where Taser guns could not be deployed. Their most recent use was by Norfolk police on 9 August during a domestic incident, according to the Association of Chief Police Officers.

The National Campaign Against Fees and Cuts (NCAFC) has organised the march on the first anniversary of the demonstration in which the Tory party headquarters on Millbank were trashed by student activists.

The Guardian has learned that groups engaging in direct action are likely to break off from the march at different points, causing disruption which may become a focus of police attention.

March organiser and NCAFC co-founder, Michael Chessum, said: "What the police are engaged in is a cynical attempt to stop people from attending the demonstration and to pre-criminalise the protest … they should be getting on with their job to facilitate protest," he said.

• The picture caption on this article was amended on 9 November 2011: the protest was in November 2010 not July 2011