Reports have emerged that one of the TU-95 Russian bombers, which flew along the western and southern coast, was carrying a nuclear warhead designed to seek and destroy submarines.

Norwegian military sources told the Barents Observer, which reports on the Baltic States, that they had intercepted cockpit conversations confirming the bomber had a nuclear payload.

The Norwegians scrambled F-16 fighters and followed them out of their airspace. They were then intercepted by British Typhoon jets off the Hebrides, which shadowed them to the west coast of Ireland.

The bombers then entered Irish-controlled airspace and doubled back towards Britain, before they were intercepted again in the English Channel.

The Norwegians informed the British, who are also members of Nato. A report in The Express in Britain stated that sources within the UK’s defence minister and RAF confirmed the bomber, at times escorted by MIG jets, was carrying a nuclear weapon.

It said Prime Minister David Cameron and his defence secretary Michael Fallon were alerted by Norwegian officials.

It quoted one senior RAF source who said: “We downloaded conversations from the crew of one plane who used a special word which meant the would-be attack was a training exercise.”

It was reported that the missile was not armed and the aircraft’s crew would have required a direct order from Russian leader Vladimir Putin before making it live.

A spokesman for the Russian embassy said he didn’t have any information about the accusations.

He said they had earlier given an explanation to the Irish Department of Foreign Affairs.

“Our planes did not violate Irish sovereign airspace. We didn’t violate international laws.”

Security expert Dr Tom Clonan said reports that the bomber was carrying a nuclear weapon were worrying.

He said that if the plane developed mechanical trouble, ditched in the sea, or had to crash, there could have been serious environmental implications.

“The idea of carrying such weapons through a busy airspace beggars belief. If there was a psychotic episode onboard and the weapon was detonated it would send out a massive electromagnetic pulse before the mushroom cloud which would destroy onboard communications systems on potentially dozens of passing commercial aircraft,” Dr Clonan said.

“These planes would be disabled in mid-flight and could potentially lead to the loss of countless lives.”

Fine Gael TD David Stanton, chairman of the Oireachtas defence committee, said it was unacceptable for the Russians to fly in our airspace unannounced and with their transponders turned off.

He said he expected that and the reports about the nuclear arms to be raised by the Department of Defence with the Russian ambassador.