Voters in Britain are not seized of the implications for Ireland of the looming Brexit referendum on EU membership, former British government spokesman Alastair Campbell has said.

Mr Campbell, who was a leading adviser to former Labour prime minister Tony Blair, said he believed Irish people could make the case for Britain to stay in the EU via connections in business and with family and friends.

“The only people who have got a vote are the British electorate, but it’s a very, very significant event for the Irish economy and Irish people,” he said.

“So I will be urging the people there to take an interest and, if they can, to get involved.”

Mr Campbell, who will address Ibec’s CEO conference on April 21st, said there was a sense in the Scottish independence referendum that many people around the world believed that vote mattered.

“I’m making a guess here but most of the Irish business community are probably for Britain staying in. A lot of people I meet are saying ‘God, I hope Britain doesn’t leave. I think that does have an impact.”

At issue in the campaign was whether undecided voters would opt to vote for Brexit or to stay in the EU.

“You’ve got this slew of people in the middle, who haven’t decided, they’re the ones you’ve got to pitch arguments to.”

A key challenge for the Remain campaign was to challenge the “lie machine” of pro-Brexit media, he said.

“The other side of the campaign has got to demolish that day after day after day.”

The undecided constituted a “sizeable minority” of the electorate, certainly enough to swing the vote.

“Are people conscious of the fact that we don’t actually know what’s going to happen to the [Irish] Border, for example? What happens? I don’t know.

"I'd be very surprised if people in middle England are thinking about that or even caring about that."

On whether the Irish authorities could do anything to influence the outcome, Mr Campbell said he would not overstate the scope for that.

"Other countries have to be very careful. As a minimum, countries around Europe have to be very clear that this can impact them as well. They should give their opinion as to what the consequences are, even for the UK."

He noted, however, that French president François Hollande had been attacked for saying the unpicking of EU treaties in the event of a Brexit would be far bigger than any change of government.

It would be wrong, he said, for anyone to assume British voters would decide in the end to remain in the EU.

“The thing about conventional wisdom is it’s almost always wrong. We’re talking about millions and millions of people taking a very important decision for billions and billions of reasons.”

At issue ultimately was the question of mood and momentum in the campaign.