A judge has condemned as "a scandal" the "wholly inadequate" prison security that allowed an inmate to import at least eight Skorpion submachine guns into Britain from Germany using Parcelforce.
Judge David Farrell QC called for an inquiry into security arrangements at HMP Wandsworth as he sentenced a couple for their roles in the plot.
Five of the guns, which are similar to a weapon reportedly used by one of the terrorists behind the Paris attacks, are unaccounted for and could be in the hands of criminals.
Ringleader Alexander Mullings secretly masterminded the smuggling operation from the prison in south-west London between January and June last year.
The 23-year-old, who is originally from Islington, was serving a sentence for a series of robberies at the time he used a mobile phone to arrange the importation.
The judge told him: "It is a scandal that the security at Wandsworth was so wholly inadequate that you were able to do so."
He said later: "I am extremely concerned that Mullings was able to commit these extremely grave offences from his prison cell at Wandsworth Prison ... having been found under the law as it then was to be dangerous.
"It frankly beggars belief that someone could so easily and quickly obtain mobile phones and then conduct such a criminal enterprise whilst in prison.
"Wandsworth prison on the face of the evidence have blatantly failed in their duty. This could only be the result of either inadequate security, incompetence or worse dishonest members of staff. I make no judgement on this.
"Clearly an inquiry is called for in order to assure the public that that prison is effective in protecting the public from dangerous criminals such as Mr Mullings."
Three of the firearms and dozens of rounds of ammunition were seized by police last year but five more packages are known to have slipped in.
Judge Farrell said: "It would follow that it's right that at large in the public domain are highly lethal, highly dangerous weapons, possibly with ammunition, for one purpose - that is to kill or maim."
Mullings, 23, was jailed for life with a minimum term of 10 years after he was convicted of conspiring to possess firearms with intent to endanger life following a trial last month.
His girlfriend Emily Ciantar, 20, who he used as a courier, was jailed for 12 years and four months after being found guilty of the same charge.
Sentencing them at Luton Crown Court, the judge said: "Each of you played a part in what was a well organised and precisely executed criminal enterprise to import machine pistols and the ammunition for them.
"Guns kill and maim, terrorise and intimidate. In the hands of drug dealers, robbers or worse they are highly dangerous. It is not exaggerating to say that people may well be killed or seriously injured as a result of what you did."
Spencer Inglis, 24, of Mitcham, south London, who took delivery of one of the guns, was jailed for seven-and-a-half years for possessing a prohibited weapon.
All the guns, which cost between £2,000 and £3,000 but had a higher street value, were deactivated weapons that the supplier had reactivated.
Skorpion submachine guns are semi automatic, rapid fire and high powered weapons. They are small and easy to conceal for a criminal.
Reports suggest that Amedy Coulibaly was armed with a Skorpion when he attacked a kosher supermarket in the French capital.
Detective Chief Inspector Rebecca Reeves said: "These are some of the most dangerous weapons I have ever seen reach the hands of UK criminals.
"Since the defendants were arrested, we have continued to investigate, in order to track down any remaining weapons that may have been brought into the country in the same way.
"Consequently, a number of additional arrests have been made and further firearms recovered as a direct result of inquiries stemming from Mullings and his network. These investigations remain ongoing.
"We have also recovered thousands of rounds of ammunition. I have no doubt this has prevented shootings from taking place."
Ciantar, of Holloway in north London, wept throughout the hearing.
The judge said he believed she would not have found herself in the dock if it were not for her relationship with Mullings.
He added: "Her role was a key role. He (Mullings) needed somebody on the outside to do his bidding."
Inglis was sentenced on the basis that he was not part of the conspiracy.
Sally Hopkins, of Royal Mail Group, which owns Parcelforce, said: "Where Royal Mail Group has any suspicion that illegal items are being sent through any of our networks, we work closely with the police and other authorities to assist their investigations and to prevent such activities from happening.
"We are not able to give any further details about our security measures as this would compromise our operations."
Prisons Minister Andrew Selous said: "We will never tolerate the use of mobile phones in prisons and will continue to clamp down on their illicit use.
"Our range of tough security measures has already successfully seen the number of seizures increase, but our proposed new legislation in the Serious Crime Bill will significantly increase our ability to tackle this problem.
"By ordering a phone to be cut off once it is identified, we will be able to reassure victims and prevent further criminal activity faster and wider than ever before."