As a Peruvian army captain in full uniform looks on, I am squinting down the viewfinder of the "Serpent", the first shoulder-launched multipurpose assault weapon I have ever handled, its crosshair fixed on a tank 291 metres in the far distance, my thumb poised on the fire button.

"Just send that right down and give someone a bad day," says Brian Gaume, the man selling Serpents to those with a few millions to spare and an itchy trigger finger. I duly do, and on the simulator plasma screen in front of me a little green pixellated tank is duly obliterated.

At the Defence Security and Equipment International arms fair in London's Excel Centre, there is no shortage of options for dishing out bad days, weeks, months and whole lifetimes.

The Defence Secretary, Liam Fox, addressed the delegates yesterday morning, extending a warm welcome to the various invitees, among them military procurement officers from Angola, Bahrain and Saudi Arabia.

The 65 national delegations asked to buy weapons in London include 14 regimes defined as "authoritarian" by human rights groups, who have highlighted the use of British arms in suppressing opposition movements in the Middle East. Dr Fox said the fair had brought together more than 1,300 defence and security suppliers – "everything from traditional defence platforms to cyber-security and counter-terrorism to commercial security, fire protection and safety". But it doesn't feel that safe. And for the thousands of military and trade delegates who will visit the exhibition this week, this is clearly a fun day out.

The halls are packed, the lunch queues terrifyingly long. Only the ladies toilets are mysteriously deserted. Next year, the same hall will host the Olympic tae kwon do and boxing contests. But this week it is not the place to be for those interested in hand-to-hand combat.

Next to the Serpent, one of many developments from Raytheon UK, the British arm of the US defence giant, is the Paveway IV, a 500lb laser-guided bomb. "It can be programmed to explode underground, to explode over a particular car or tank, or to take out a particular floor of a building," says Nick West, the company's communications director. Over the past few months, the Paveway IV's lasers have been set to guide its missiles from allied jets into strategic targets all over Libya.

On the canals outside, huge battleships are moored, and lucky delegates race around in interceptor boats, complete with anti-tank guns and surface-to-air missile defence systems. A little like the Venice Biennale, arms companies are grouped nation by nation in their own "pavilions". The Israel Pavilion looms large, but the USA Pavilion is something to behold. Men in full SWAT uniforms stand between rack after rack of machine-guns.

"Securing Nations Around The World" is the slogan of AeroVironment Inc, a company which produces "unmanned aircraft systems". To the layman, they look a lot like drones, although, as more than one "unmanned aircraft system" manufacturer said, "we don't use that word". They can be used to target "ships, tanks, or terrorists", yet the promotional poster shows an unmanned aircraft flying above Wembley Stadium – perhaps an extreme solution to the England football team's recent difficulties.

It is not hard to spot the VIPs. They mostly wear military uniform, with big red badges saying "delegate", and wander in packs. Those from Ukraine seem particularly intimidating. The officials hold purse strings for some of the world's biggest budgets.

The UK defence industry's section is vast and sophisticated. BAe Systems is exhibiting Adaptiv, a kind of invisibility cloak that can make a giant tank look like a simple car on enemy detection systems. "There are economies of scale at work," said a spokesman for UK Defence. "If the Government can help a UK company to sell big numbers of its products abroad, that company can sell them to the Government for cheaper."

Yet it seems hard to strike a deal. Not one stand will countenance any discussion of price. "I'm forbidden to talk about that," is a familiar refrain.

It is not the only instance of caginess. The Israeli weapons industry's stand is lined with Tavor automatic and semi-automatic rifles. "They are used in Israel and 60 other countries," a spokesman says, but refuses to say which ones. "We cannot discuss clients but go on YouTube and you will see some interesting stuff."

The man from Glock sits behind a desk littered with revolvers. Nearby, two Portuguese delegates are aiming pistols at one another, yet my notepad seems to be the most terrifying thing the salesman has ever clapped eyes on. "I cannot say anything, I cannot say anything," he repeats.

Next door, the Swiss munitions firm RUAG is similarly elusive, but its display boasts that it makes "the UK MOD's preferred hand grenade".

The new Scout tank from General Dynamics is also here, one of four new models that will become standard British Army equipment by 2020. Even in these austere times, the 500 to 600-tank contract will cost up to £2bn. After a couple of hours here, that feels like a drop in the ocean.

A booming industry

* The UK has the world's second- largest defence and security sector; only the US sells more weapons and military hardware worldwide. The British share of the global market increased from 18 to 20 per cent in the past year, according to the government body UK Trade and Investments.

* The industry was worth £22bn to the British economy in 2010, the defence trade group ADS (Aerospace, Defence and Security) claims – £9.5bn of which was in exports.

* Saudi Arabia is by far the biggest buyer of British weapons and also the largest importer of arms globally. Saudi contracts earned the UK about £300m last year, according to arms trade analysts the Stockholm International Peace Research Institute.

* Behind the Saudis, the US has the most defence contracts with British firms. India, which imports 70 per cent of its military equipment, represents the UK's third-largest arms market.

* Bahrain, which was controversially invited to this week's DSEi exhibition after its regime crushed an uprising in February, signed contracts with British firms worth £2.4m this year, according to figures obtained by the Campaign Against the Arms Trade.