Seventeen anti-tax avoidance activists have been singled out for prosecution by the Crown Prosecution Service for allegedly attempting to promote their cause with leaflets and banners during a protest at Fortnum & Mason, London, in March.

The group of campaigners from UK Uncut all entered not guilty pleas as they appeared at Westminster magistrates court charged with aggravated trespass at the luxury food store in Piccadilly on 26 March.

The protest was described by a senior officer who attended the scene at the time as "non-violent" and "sensible".

Robert Short, for the CPS, told the court that the prosecution of a total of 30 Uncut activists, whose trials have been split into batches, would continue despite charges being dropped against 115 others.

Defence solicitors, however, revealed a possible split within the CPS as they told the court that the London head of prosecutions, Alison Saunders, had still not confirmed whether even these 30 cases would be continued.

Explaining to the court why the group had been selected for prosecution, Short said: "This group were in possession of materials [which] enhance the aggravating factors". Describing the materials as "banners, cordon tape, and leaflets", Short added that the CPS believed a number of defendants had "leaflets in bundles or piles on their possession on arrest".

Short told district judge Michael Snow that the Crown believed this signalled their "intention to promote their cause".

Querying the decision, Snow said it was "quite legitimate to promote their cause" and asked why it was criminal to do so with leaflets.

Short agreed that the act of possessing leaflets was not itself criminal but it had been used by the CPS as "a measure to filter proceedings". It suggested that the defendants had been part of the "organising element". "They had the means to play a more significant role on the day," he said.

A defence solicitor, Mike Schwarz, complained that there was not a consistent approach to selecting defendants for trial.

Defence solicitors also revealed that they had notified the court that abuse process proceedings had been launched involving promises made by chief inspector Claire Clark. They will allege that the senior officer made false promises to protesters when she told them that they would be free to leave Fortnum and Mason, despite knowing that they would all be arrested as soon as they stepped outside.

The court confirmed that six senior officers from the Metropolitan police would be called to testify. Snow had previously warned that the trials could leave the Met "headless" for weeks.

The first trial of 13 defendants will be heard on 10 November. The second trial of 17 defendants had to be split into two because the court was told there was not enough space in the dock at the new facilities in Marylebone which open next month. Those trials will begin on 5 and 19 March 2012.

Today's defendants included a youth worker, two students, a filmmaker, a charity worker and a web designer. All were adults aged under 30. Around 30 supporters were outside the court room.

• Shiv Malik will be speaking at the Edinburgh Book Festival on Sunday at 6.45 at the Peppers Theatre about his book Jilted Generation.