By Stuart Ramsay, Chief Correspondent
As Britain's security services warn of potential Paris-style terror attacks in the UK, Sky News has been told by eastern European mafia gangs that demand for their military grade weapons across Europe has rocketed in two years - and they will supply to anyone.
Security analysts say Islamist terror cells and "lone wolf" killers now consider automatic weapons the best way to bring mass murder to our streets.
Europe's open borders mean that weapons like the AK-47 can be moved easily to the buyers in western Europe.
The AK is the most requested weapon according to the gangs - a weapon rarely used by ordinary criminals.
The gang took the Sky team to a deserted forest in Romania
From the mountains of the Balkans across huge, remote forest lands in eastern Europe, networks of gangs have access to millions of weapons that have been cached after years of conflict or are in general supply in areas bordering conflict zones such as Ukraine.
After months of negotiation with a Romanian gang Sky News was directed to a remote part of the country for a meeting with gang members prepared to show us what they could supply.
There is no subterfuge here. They knew we were a news organisation wanting to illustrate how getting a weapon is relatively easy and they believed we were going to buy them.
We did not, which made matters a little tricky.
The point is they didn't care who we were if we were prepared to pay. Throughout our meeting they made it clear they would sell to absolutely anyone; bank robber, mass murderer or terrorist, they made no distinction.
Video: Gun traders show Sky's Stuart Ramsay the weapons they have for sale
We had been told that at a certain point on the route to the meeting point a 4x4 vehicle would be parked on the opposite side of the road and would flash its lights, signalling us to stop.
We were instructed to remain in our car and to make no attempt to film or approach the passengers in the vehicle before reaching the final destination.
As the driver and his passenger turned their car - a battered vehicle without plates - we could see they were unmasked but wore hats and covered their faces with their hands before speeding off in a cloud of wheel-spinning dust.
We followed them along rutted farm tracks, main roads and country lanes deep into a forest with no phone signal before stopping in a clearing.
Two men, now in balaclavas, gestured for us to join them. We were searched, our equipment checked and phones removed and locked inside our car. They had taken our car key.
At the boot of their car they revealed the weapons available to buy, or rather the types of weapons. They assured us they could supply thousands of guns and crucially the ammunition to go with them.
"We bring them from Ukraine with the ammunition, as much as you want," one of the men said.
The men claimed their weapons are smuggled from Ukraine into Romania before being shipped by another gang to western Europe and the middle east.
Also available for sale was this sniper's rifle for 3,000 Euros
But western Europe was the primary destination.
The men said they only dealt with firearms but they had close links to another gang that specialised in heavy weapons, grenades, rocket-propelled grenades and mines.
Among the weapons on display were high quality, apparently brand new, sniper rifles. One, going for 3,000 Euros (£2,540) was an Austrian military Steyr rifle complete with a top-end sight.
Other weapons included semi-automatic rifles, shot guns, hunting rifles and pistols.
In pride of place was a mint condition AK-47. This weapon they said was their biggest seller at 1,700 Euros (£1,440) and demand from Europe over the past two years had soared. The AK-47 is the terrorists' weapon of choice.
The increase in murderous terror attacks in Europe has highlighted the damage that can be done by military grade weapons in the hands of individuals and gangs. Europe is awash with illegal guns and the Shengen border treaty makes it virtually impossible to track or stop their movement.
Traditionally, terrorist attacks were characterised by the use of bombs. Not any more. Automatic weapons kill more people, are easier to transport and far easier to use.
Across Europe and the UK security services now find themselves on constant alert. In London we showed film of our meeting to officers of the National Crime Agency (NCA).
Video: Deadly Terror Attacks In Paris
They confirmed that the types of weapons, the location of the meeting and prices discussed were in line with their intelligence.
"The weapons are often sourced near conflict zones like Ukraine, which is where your meeting took place," said Ian Cruxton, Director of Organised Crime at the NCA.
"I have to stress that the UK is by far the safest place in Europe when it comes to attacks with weapons like this. But we have to be vigilant, we always have to do more," he said, pointing out that the Europe border is only 21 miles away.
Back in Romania the gang members made it clear that if we were not going to buy they were not going to hang around.
Before driving away they told us to wait for 20 minutes to allow them to disappear. "If you come again, you must buy or don't come," one of them said as they left.