GETTY The IRA and ISIS are working together, according to UKIP's Northern Irish leader

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David McNarry, the chair of the Northern Irish branch of Ukip, revealed to Express.co.uk a growing partnership between the two terrorist groups in Ireland which he labelled "extremely worrying." He said: "I’ve spoken to security people, some old timers. What they were most interested in was how ISIS was developing car bombs." He said the switch from the jihadis’ suicide attacks to car bombs was due to bomb-making lessons from former Provisional IRA members, known as Provos, in the Republic of Ireland. McNarry said: "Provos never strapped body bombs to themselves. The people I spoke to were keen to stress it was very likely they had learned how to make car bombs from Provos. These were people I trust. "Car bombs are more lethal. Suicide bombers announce themselves almost, but car bombers don’t. I know from experience, as does anybody who has lived through the terrorist activity here, that you can bomb the hell out of a city."

GETTY IRA gunmen in 1977. Though most have given up their arms, small factions still continue

An ISIS cell operating in the Republic of Ireland, he said, was very capable of launching an attack on mainland Britain with their new IRA bomb knowledge. Due to the porous border with Northern Ireland and readily-available ferry services across the Irish Sea, McNarry said jihadis would have no trouble making their way from Dublin to England, Scotland or Wales. He said: "We have the poorest border in the world. We know that from the old Provo activity. No-one can cross the border better than the IRA. They would cross in the dark of night, commit their dastardly deeds and then go back."

IG David McNarry, chair of Ukip's Northern Irish party group

The border just isn’t there. It’s so easy to be breached. I'm sounding alarm bells. We're on alert, be careful David McNarry

When asked whether he feared that Ireland was being used as a base for an attack in mainland Britain, as Belgium was for the November terror attacks in Paris which left 130 dead, McNarry said: "That's my big fear." He revealed that busloads of "foreigners" were regularly driving from Dublin across the border to Larne in Northern Ireland, where they boarded ferries to Scotland and "disappeared." McNarry said: "How easy it is for people to be crossing the border - the border just isn’t there. It’s so easy to be breached. I'm sounding alarm bells. We're on alert, be careful." He warned that Ireland's history of terrorism made it a perfect base for a European ISIS cell. He said: "Ireland has never lost its criminal society. Terrorism in Northern Ireland was and is criminal activity. "But the new threat is ISIS. Terrorism is a shared world and technology and capability will be shared."

GETTY A building in London's Docklands lies in ruins after an IRA bomb attack in 1996

GETTY Most ISIS attacks have used suicide bombers rather than car bombs, which were favoured by the IRA

Terrorism in Ireland has been in decline since the 1998 Good Friday Agreement, in which most dissident groups disposed of their weapons, but has recently experienced a small resurgence. Last month, a prison officer in Belfast died following a car bomb attack carried out by the New IRA, a splinter nationalist group that does not recognise the ceasefire. With the country currently celebrating the centenary of the 1916 Easter Rising, in which rebels claimed independence from Britain during an armed rebellion in Dublin, fresh warnings have been issued to visitors to the island. The Australian government told its citizens to be wary of "increased tensions" in the country, while the UN has advised tourists to avoid protests or demonstrations.