A "committed" terrorist who infiltrated the British military has been jailed for 18 years for supplying bombs to dissident Irish republicans.

Former Royal Marine Ciaran Maxwell stashed anti-personnel mines, mortars, ammunition and 14 pipe bombs - four of which were later used - in 43 purpose-built hides at eight locations in Northern Ireland and England.

Bomb-making materials were found in barrels and buckets buried in the ground as well as an adapted Police Service of Northern Ireland (PSNI) pass card, a PSNI uniform and a police stab-proof vest.

The 31-year-old, who is originally from Larne in Co Antrim and was with 40 Commando based at Norton Manor Camp in Taunton, Somerset, at the time of the offences, pleaded guilty to preparation of terrorist acts between January 2011 and August last year, possessing images of bank cards for fraud and possessing cannabis with intent to supply.

PSNI Detective Chief Inspector Gillian Kearney said Maxwell used his military know-how to accumulate and construct his devices, and described the infiltration of the military by a republican terrorist as "very unusual" and "certainly the first case of its kind in recent years".

Police also fear weapons he constructed may still be in circulation, ready for deployment by dissident republicans, with some of his stash potentially able to make an explosive larger than the 1987 Enniskillen bomb.

Sentencing, Mr Justice Sweeney said: "I'm sure that you were and will remain motivated by dissident republican sympathies and a hostility to the UK.

"There was sophisticated offending on a substantial scale which took place over a period of more than five years.

"There was clearly the potential for the deployment of many bombs of varying types and sizes against multiple targets, with the ultimate intent of those planting the devices being to kill.

"There was considerable planning, including attack planning, research, and the acquiring of large amounts of materials including police items for use in disguise.

File photo issued by the PSNI of a barrel containing weapons recovered from a 'terrorist hide' in woodland at Capanagh Forest near Larne in Northern Ireland.

"You were strongly committed to the cause."

Maxwell was handed an 18-year jail term with another five years on licence.

He was given an 18-month sentence for possessing cannabis with a street value of £8,100, and two years for fraud. Both sentences will run concurrently.

Maxwell, described by the judge as an "inveterate record-keeper", showed little emotion as the sentence was handed down.

The Old Bailey heard that the father-of-one researched targets and discussed plans to attack police stations and officers.

His plot, however, was foiled when members of the public stumbled across his weapons hides by chance.

DNA evidence found on parts of the haul led them to Maxwell, who was on the national database due to his alleged involvement in an unrelated assault case.

Paul Hynes QC, defending, told the court his client was not ideologically driven and would not have used violence for a cause.

Greenhouse used by former Royal Marine Ciaran Maxwell at Powderham New Plantation

He said it was Niall Lehd, said to be a member of the Continuity IRA (CIRA), who was the "instigator" of a joint venture with Maxwell, who had "no long-lasting republican ideology".

The judge said there was "no doubt" Maxwell carried on with his work after Lehd was jailed in 2014.

He added: "To state the obvious, a skilled bomb maker is of considerable importance to a terrorist organisation like the Continuity IRA."

The judge said some of the ammonium nitrate recovered in Northern Ireland could have been used to make an explosive larger than "the notorious Enniskillen bomb", the Poppy Day bombing in 1987 which killed 11 people and injured 63 others.

Maxwell denied joining the Royal Marines in 2010 with the intention of infiltrating them.

He claimed he faked his support for the dissidents' cause because he was "frozen" with fear and believed old connections wished "serious ill" on him and his extended family in Northern Ireland and England.

The court also heard that he had been brought up as a Catholic in a largely loyalist town and suffered a fractured skull as a 16-year-old when he was the victim of a sectarian attack.

Maxwell, who had been living in Exminster in Devon before his arrest, was due to be promoted to corporal before he was dismissed from the service.

Responding to the sentence, PSNI Assistant Chief Constable Stephen Martin said: "These items are designed to cause damage, serious injury and to kill.

"As a result of these finds, and the arrest and sentencing of Ciaran Maxwell, there is no doubt in my mind that Northern Ireland and England are safer places to live."