Police have seized more than 800 potentially lethal weapons during a month-long operation designed to prevent terrorists and criminals gaining access to illegal firearms, amid fears of a Paris-style gun attack on the streets of Britain.

At least 379 of the 833 guns have been confirmed as viable – 440 are still awaiting assessment – more than 40% of the total seized last year, a figure those leading the operation put down to the intensity of the operation, rather than any surge in weapons in the UK.

The initiative, led by the National Crime Agency (NCA) and Scotland Yard’s counter-terrorism (NCTP) command, is the largest multi-agency programme that has ever been mounted.

Det Supt Nick Wilcox, from NCTP, said the aim was to “make it harder for anyone to access firearms. If we do that we will achieve our objective of preventing terrorists access to firearms”.

It was launched as part of attempts by British law enforcement, security and intelligence services to try to prevent a marauding terrorist gun attack such as the one in Paris in November 2015, which killed 130 people, happening in the UK.

Although none of the 282 suspects arrested during the four-week operation have been directly linked to terrorism, the operation did yield a “handful” of counter-terrorism leads.

Police also believe it has helped them understand the threat posed, to disrupt it and identify links between criminal groups and individuals.

Wilcox added: “We’ve found there are associations and potential links between CT [counter-terrorism] suspects and firearms … It’s allowed us to create a picture of who is associated with who and where the threat may lie.”

Wilcox stressed that the UK still benefited from low availability of guns because of firearms legislation and the fact that it is an island.

The haul, recovered on mainland Britain in a four-week period in October/November last year, included a fully loaded AK-47 assault rifle, among 11 assault rifles seized, a Skorpion sub-machine gun and two machine guns. Police also seized about 80kg of drugs, £575,000 of cash and 4,385 rounds of ammunition (about half of that in the London/West Midlands region).

Of the 282 people arrested, 111 related to firearms offences and 16 have been charged so far.

As part of the initiative, officers encouraged the public to report information and, as a result, received more than 160 tips via Crimestoppers, which combined with other sources led to an average of 55 intelligence reports every day into the operations room.

The NCA and NCTP will continue their cooperation on the threat posed by guns through a new multi-agency intelligence-sharing hub.

NCA’s deputy director, Chris McKeogh, said he believed the month-long initiative had had a significant impact. Asked if it had made it harder for a Paris-style atrocity, he said: “I hope so … If you are someone bent on committing a terrorist atrocity we are going to make every effort to deny you the opportunity to get a firearm.”