Brian Cowen sent a voicemail to 15,000 activists in his Fianna Fáil party on Monday night as the Irish prime minister stepped up pressure for a big turnout in Thursday’s critical referendum on the Lisbon reform treaty.

The performance of the Fianna Fáil political machine, with an official membership of 65,000 and 3,000 branches across the country, could determine whether the treaty is passed or defeated.