Mass email petitions to TDs and senators may be blocked after a million messages were sent to the Houses of the Oireachtas by campaigners seeking to have a vaccine for cervical cancer reinstated.

The so-called mail storm caused major difficulties for TDs and other staff, who were unable to access email as their computer systems and Blackberry phones ground to a halt.

Forty thousand euro had to be spent to increase computer capacity to ensure government networks could cope if it happened again, the Sunday Tribune has learned.

Consideration is now being given to blocking inbound emails from campaigners if it appears a concerted effort is being made to create a mail storm.

The cervical cancer petition was organised by Today FM host Ray D'Arcy who helped spearhead the failed campaign to reinstate the vaccine.

In November, the Department of Health had abandoned a plan, announced just three months earlier, to vaccinate all 12-year-old girls against a virus that causes cervical cancer.

Citing "very scarce" resources, health minister Mary Harney said the annual cost of the programme, which could have saved up to 80 lives a year, would be about €9.7m.

An email briefing to party whips, written by the clerk of the Joint Administration Committee, Pat Haran, said: "In November 2008, members of the government side of both houses were targeted in a mail storm...This made it difficult to use the email database on a PC and it rendered Blackberries completely unusable as it is not possible to process that volume of inbound memos on the small screen of a Blackberry. Approximately 110 members use Blackberries.

"The mail storm also threatened the Oireachtas mail systems and the ICT (Information and Communications Technology) Unit was forced to replace mail servers overnight in order to avoid a collapse of the email system.

"This mail storm was relatively small, as it was orchestrated by only one radio station. If broader orchestration occurred, the result would probably cause some systems collapse unless ICT unit is authorised to respond in some way."

TDs and Senators have been told that all of them must agree to the proposal as it would not be possible to block emails individually.

The briefing note said "blocking would apply only to memos, which form part of a mail storm, and members would be notified when blocking commenced".