Activists accused of occupying the luxury London food retailer Fortnum & Mason during tax avoidance protests in March are expected to plead not guilty to charges of aggravated trespass on Tuesday.

The case against five minors arrested during the UK Uncut demonstration was dropped by the Crown Prosecution Service last week but charges remain against 139 others.

Of those, 13 are expected to enter pleas at City of Westminster magistrates court on Tuesday, when a trial date should also be set.

Lawyers are pressing for the charges to be dropped against all those arrested after the occupation of the store. Mike Schwarz, a partner in criminal law at Bindmans, which is representing most of the accused, said his firm had written to the CPS arguing that it was in the public interest that the charges be withdrawn as they interfered with the right to peaceful protest.

Similar concerns have been expressed by Liberty and by the Labour MP John McDonnell. Liberty said it "deplored" the offence of aggravated trespass, while McDonnell told the Independent that any trial would be "outrageous" and "fly in the face of public opinion".

Activists have also raised concerns about the way in which the arrests were carried out. Police officers at the scene described the occupation, which took place at the same time as massive public sector demonstrations against government cuts, as "non-violent" and "sensible".

Activists said the police tricked them into a mass arrest after giving assurances they would not be detained. In video footage obtained by the Guardian, a senior officer tells UK Uncut protesters that police are making sure it is "clear and safe" before letting them leave. Upon leaving the building the activists were kettled and arrested one by one. Some were held in cells for up to 24 hours.

Raj Chada, a partner at law firm Hodge, Jones and Allen, who is representing 20 of those charged, although none of those expected to enter pleas on Tuesday, said: "This idea a senior officer told them to leave raises fundamental questions about police tactics for future public events if the police can't be trusted."