Gardaí have begun an investigation into revelations by RTÉ News that more than 20 people are due to be charged following a protest in Tallaght last November in which Tánaiste Joan Burton was trapped in her car.

Asked about the nature of the Garda inquiry, what offence may have been committed, or who the officers intended speaking to, a Garda spokesman said there would be "no further comment at this stage".

He said the investigation, which began this morning, is in the "very early stages".

It is understood the water charge protesters will face a range of offences - including false imprisonment, criminal damage and public order - in the Circuit Criminal Court.

Earlier this evening, Socialist Party TD Paul Murphy wrote a letter of complaint to the Garda Commissioner, Garda Ombudsman and the DPP about how the information came into the public domain.

Ms Burton, who was trapped in her car for more than two hours during the incident after attending a graduation ceremony at An Cosán College in Jobstown, has declined to comment.

Her car was surrounded by protesters who banged on it and chanted slogans.

Last night RTÉ News reported that over 20 people are expected to appear in court in the coming weeks in connection with the incident.

Mr Murphy said he had sent the letter of complaint to the Office of the DPP, the Garda Commissioner and the Garda Síochána Ombudsman Commission, in relation to the "leaking of the information that over 20 protesters at Jobstown are due to be charged with serious criminal offences, including false imprisonment".

He said: "The first I and other protesters heard about this was on the Nine O'Clock news last night on RTÉ."

He added: "It is quite an incredible situation whereby the media is advised of charges in advance of those due to be charged."

The TD said: "The source of the leak can only be within the DPP or the gardaí. I have therefore written to the appropriate authorities in both seeking to establish what investigations will be carried out to determine the source of the leak."

The Tánaiste has not commented on the decision to charge people with criminal offences following the incident. 

A spokesman for Ms Burton today said: "The gardaí and the Director of Public Prosecutions are independent in their functions, and it would be inappropriate to comment on ongoing proceedings."

The DPP has directed that more than 20 people be charged with a variety of offences.

More than 40 people, including Mr Murphy and two other public representatives, were arrested and questioned during the garda investigation.

Jobstown residents who were arrested in relation to the protest say they will hold a press conference tomorrow.

This morning, Mr Murphy described the decision to charge people with criminal offences as an attack on the right to protest.

Speaking on RTÉ's Morning Ireland, Mr Murphy said other protests had also delayed traffic but no prosecutions had resulted in those instances.

"It is absolutely farcical, it stretches the definition of false imprisonment beyond breaking point to suggest that because the Tánaiste was delayed in Jobstown in her car for two-and-a-half hours that that's false imprisonment.

"I mean there are multiple protests ... around the time of the Jobstown protest there were farmers blockading meat processing plants, there have been no prosecutions there ... that's why we have said that the policing here is political."

Sinn Féin justice spokesman Pádraig Mac Lochlainn said the possibility that protesters could face jail time was "highly disproportionate" and described the developments as "deeply worrying". 

Additional reporting from RTÉ Crime Correspondent Paul Reynolds

Because the decision to charge these people was taken more than six months after the event, their cases cannot be dealt with in the District Court, where penalties are at a minor level.

Those to be charged will face trial on indictment before the Circuit Criminal Court.

Unlike the District Court, cases before the Circuit Court can be tried before a jury but the penalties upon conviction are more severe.

When the trials take place will be different from when the initial court appearances take place.

What will happen pretty quickly is that people will be charged and there will be an initial appearance before a judge in the court. These are only procedural matters.

The date for trial will be a different matter.

Considering just how busy the courts are, I would be very surprised if any trials would take place before the general election.