During one incident last November four gardai and four protesters were injured after the crowd attempted to breach a security cordon and enter the refinery in Ballinaboy.

There were a number of arrests over that incident and three summonses have already been issued with more thought to be imminent. It was confirmed last week that over 20 gardai are being investigated following complaints made against them by 16 protesters.

Protests were stepped up last October when Shell resumed work at the refinery site which led to Shell staff and contractors requiring escorts to and from work.

Dozens of people gather at the terminal site each day to protest and a number of demonstrations against Shell have taken place in Dublin.

Shell is developing the Corrib field 65km off the Co Mayo coastline.

Gardai are policing the site on a 24-hour basis and it is believed that some of the more extreme activists against the gas terminal and high-pressure pipeline are under surveillance. It is estimated that this is costing around 800,000 per month.

The Garda Complaints Board has confirmed that it is investigating complaints against over 20 members of the force. The head of the Garda operation, superintendent Joe Gannon, is one of those against whom a complaint has been made.

Two superintendents have been appointed by the Garda Commissioner to investigate two complaints against Joe Gannon while a Special Branch superintendent is examining the other complaints.

Justice minister Michael McDowell has revealed that the cost of the policing arrangements at Ballinaboy up to 17 April was 5.4m. This includes overtime payments and all other associated costs.

He would not release the number of gardai or other detailed information about the policing plan "for security and operational reasons".

He said: "It is not Garda policy and it would not be in the public interest to disclose detailed information of a kind that could potentially have an operational impact on policing arrangements, including numbers of Garda personnel deployed on an ongoing daily basis and/or on stand-by."