The president of the European Commission, Jose Manuel Barroso, has refused to be drawn on whether the Irish people might be asked to vote for a third time on the Lisbon treaty should it be rejected next month.

Asked if it was possible to rule out such a prospect, he stressed the EU would respect the will of the Irish people, but said he did not wish to speculate "about negative scenarios".

"Without the agreement of the Irish people we will not have the Lisbon treaty... I'm against any kind of two classes in the [EU] countries," he added. "Look, I really think that we have to vote now Yes or No," he said. "I hope the vote will be yes, I'm really confident about it – but I don't want to speculate about negative scenarios.

"We don't need more speculation about that now. Of course we'll respect the will of the Irish people, that is for sure, as we have respected [it]. That's why we are not asking the same vote, we are asking a vote with a different formula and with different conditions."

Barroso, who was in Limerick yesterday to encourage a "Yes" vote in the October referendum, took the opportunity to launch a strong defence of the benefits which Ireland has seen as a result of its membership of the EU.

This included more than €120bn in lending from the European Central Bank, which he noted countries such as Iceland, which is outside the EU, could not avail of.

"That [€120bn] is 15% of the total of ECB lending. Being in the Euro area has provided a vital [measure of] stability for Ireland at this difficult time," he said.

"I know what's happened for instance in Iceland, where people would go to their ATM machine and they could not withdraw from it... because they were in a country that could not benefit, as you could, as you can, from European membership."

Barroso was subject to heckles by anti-Lisbon campaigners during a tour of Limerick city's milk market. As he arrived at city hall, he also announced the EU Commission has approved a grant of €14.8m from an EU fund to help 2,400 Dell workers to find new jobs.

He rejected claims by the No campaign in relation to the prospective impact of the Lisbon treaty on issues such as the minimum wage and said some of the anti-Lisbon pamphlets he has seen were "pure lies".