This week, the British government invited some of the worlds most repressive regimes to "Security and Policing", a security trade fair. The Home Office boast that this is "the only 'closed' event of its kind", so dictators and autocrats can browse stalls selling surveillance technology and crowd control equipment without anyone knowing about it.

The event is for "UK suppliers to showcase the very latest equipment" to security officers from the Gulf and elsewhere, with backing and appearances from Home Secretary Sajid Javid and Trade Secretary Liam Fox.

VICE has pieced together the evidence and gathered testimony and material from last year's event that reveals how the spyware on sale works, and who buys it.

Our investigation comes as an MP was barred from entering the fair. Brighton Labour MP Lloyd Russell-Moyle sits on Parliament's Arms Export Committee, and says he is investigating UK’s surveillance industry. Russell-Moyle was also "deeply alarmed" that he was barred from entering the Security and Policing Trade Fair, and "denied entry to a government-organised trade fare for the very equipment that we are investigating".

"The British government routinely approves the export of powerful internet and telecoms surveillance equipment to governments which hunt and, in some cases, kill journalists, activists and dissidents," Lloyd Russell-Moyle MP told VICE.

The top products on sale are "intercept" products for spying on phones, emails and other digital communications. Anglo-German firm Gamma Group are one exhibitor. They offer all levels of "communications interception". Last year, Bahraini dissidents launched legal action against Gamma, alleging Gamma sold Bahrain's government their "FinFisher" software, which infects and spies on target computers. The dissidents say the Bahraini sheikhdom then used the spyware to catch Arab Spring dissidents. Gamma Group have firmly denied the allegations, saying: "No evidence has ever been produced of any part of the Gamma Group participating in any human rights abuse by the government of Bahrain. The claim is fundamentally misconceived and will be defended."

Peter Lloyd, a solicitor representing Gamma Group, said: "The matters raised by Leigh Day in its letter of claim have been exhaustively explored in other forums. No evidence has ever been produced of any part of the Gamma Group participating in any human rights abuse by the government of Bahrain. The claim is fundamentally misconceived and will be defended."

Images from Gamma Group's sales brochures from the Security and Policing exhibition

VICE has obtained Gamma Group's sales brochures from the Security and Policing exhibition. They show the firm is marketing machinery to tap into people’s mobile phone calls. Known as an "IMSI catcher" and codenamed "Mongoose", Gamma’s machine emulates a mobile phone mast, but is "more attractive than the real network", so captures signals from targeted mobile phones.

As well as this intimate tracking of individual mobile phones, Gamma also offers a system to tap all phone calls – or even all internet traffic – entering a country. Gamma says its "Telephony Monitoring Solution" can be scaled up to tapping into 60,000 simultaneous calls, with full audio playback

Gamma also say in one movie presentation that they can intercept all IP (Internet Protocol) traffic into a nation, claiming "the system has no scaling limitation". They offer systems to analyse all this internet traffic to "discover cells, syndicates and networks" and "identify kingpins, agents and handlers".

Gamma says its internet surveillance will help identify "collaborators in your own country" working with "threats originating in foreign countries". This is exactly the kind of language the repressive sheikdoms of the Middle East used to describe political dissidents: the Gulf countries all treat Arab Spring-type dissidents as foreign-directed conspiracies.

Image from Gamma Group’s sales brochures from the Security and Policing exhibition

Britain’s biggest arms firm, BAE Systems, have also become the UK’s leading "lawful interception" company. BAE offer these snooping systems based inside national telephone companies. VICE has obtained details of BAE's sales patter from last year's Security and Policing conference.

An engineer working with the company said BAE worked with Gulf Cooperation Council countries – meaning Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates. The source said, "Obviously we do work very closely with Cheltenham, who know everything we do" – Cheltenham meaning the UK government spy centre, GCHQ.

A BAE spokesperson told VICE: "As a global company, BAE Systems has operations in numerous countries, and we comply with all relevant export control laws and regulations in the countries in which we operate."

A page about more traditional bugging systems. Image from Gamma Group’s sales brochures from the Security and Policing exhibition

Also exhibiting is Italian firm IPS (Intelligence and Public Security), which sells to "Homeland Security Departments, intelligence and law enforcement agencies that need to intercept, collect and deep analyse heterogeneous data such as phone calls, internet traffic, data coming from tactical devices and third party databases".

Such surveillance could be dangerous in the hands of authoritarian regimes. The UK licenses the sale of surveillance kit to "friendly" but undemocratic nations in the Gulf. But when Al Jazeera approached IPS in an undercover investigation, IPS told a reporter posing as a potential buyer looking for an Iranian deal, that the firm was "OK with Iran" and that they could "manage" any "export restriction" by dressing up their internet "intercept system" as a "traffic management system".

In response to these allegations, IPS told Al Jazeera that they operate with full respect of the regulations. They added: "We had no intention of completing this or any deal with the individual our staff met with. Any deal that we may have discussed with him would have to be dependent on obtaining the full legal authorisation from the authorities."

Image from Gamma Group’s sales brochures from the Security and Policing exhibition

VICE approached the Home Office, Gamma and IPS, but all declined to comment.

Security and Policing ran from the 5th to the 7th of March at the Farnborough Exhibition Centre – part of the complex near London that usually hosts the Farnborough Airshow, itself an arms fair selling warplanes to foreign delegations.