A Royal Marine reservist is facing a "considerable" jail sentence after admitting charges linked a cache of firearms, grenades, plastic explosive and ammunition.

Martin Shannon, 43, was arrested near Winchester on September 1 this year after an undercover operation headed by the National Crime Agency (NCA).

The married defendant, who was said to be suffering from post traumatic stress disorder, admitted 15 firearms and explosives offences at the Old Bailey today, including selling some of the guns during the covert operation.

It was heard he acquired nearly all the arms in his role at RM Poole.

Shannon, of Hayley Close, Hythe, near Southampton, pleaded guilty to transferring an assault rifle, pistol and sawn-off shotgun as well as shotgun cartridges.

He also admitted having more than 1,400 rounds of ammunition, seven hand grenades and plastic explosives which were uncovered following his arrest.

Defence barrister Kevin Hill said Shannon had a psychiatric history which may offer some mitigation in the case.

He told the court: "The concern is post-traumatic stress disorder that may well have some bearing on sentence in this case in terms of mitigation available.

"It is a case where there might be significant mitigation that would assist the court in the form of psychiatric assessment.

Judge Marks agreed and remanded the defendant in custody until sentencing on December 16.

He told the defendant: "It is intended a psychiatric report be obtained to understand something about your background, in particular it is said that you may be suffering from PTSD that may impact on these offences.

"In the meantime, you will need to remain in custody and I am sure you will understand the fact I am adjourning for a report is not an indication that the case will be dealt with in any other way than immediate imprisonment.

"The only issue will be as to the length of the sentence."

At the time of his arrest, Rob Lewin, head of specialist operations at the NCA, confirmed there was no link to terrorism.