Boris Johnson has launched a robust defence of the DSEI arms fair, as critics warn that Russia should be banned from attending the London arms show as the state's arms exporting wing has supplied Syria's Assad regime.

Speaking to the Huffington Post UK, the London Mayor said that the "Defence Security Equipment International" trade show, which will see nearly 30,000 people from around the world flock to London's Excel Centre from Tuesday, helped countries get their hands on "legal weapons".

Arms campaigners have warned that the fair would allow "brutal dictators to shop for weaponry". However, Johnson said any concerns were "centuries old".

The Mayor said that Britain's involvement in the arms trade was useful as it was "sensible" as a way to provide "legal weaponry" to governments, with Britain "an expert at making some of them".

The DSEI arms fair, the world's largest weapons show, is supported by the UK government's Ministry of Defence and UK Trade & Investment (UKTI).

The Mayor told HuffPostUK: "This is an argument that is centuries old and thankfully global conflicts are diminishing in number, but insofar as it is necessary for govenrments and authorities to be properly equipped against those who mean them and their people harm, it is only sensible to have legal weapons. It so happens that this country is an expert at making some of them."

Politicians and arms campaigners have reacted with fury to the presence of Russia's state technology wing ('Rostec') at the fair, since its export company Rosoboronexport has supplied weapons to the regime of Syrian President Bashar Al-Assad.

An internal letter released by Human Rights First from the Syrian High Command's Army Supply Bureau to Rosoboronexport, suggests that President Bashar Al Assad's regime had made new orders for rifles, machine guns, grenade launchers, mortor rounds and ammunition.

Tory MP Brooks Newmark, a member of the Treasury select committee member and supporter of the Syrian opposition, said: "Given my understanding of Rosoboronexport's role in the Russian defence industry and their role in providing missiles to the Assad regime, my belief is that Rostec's invitation to the forthcoming fair should be revoked forthwith."

Labour MP Ann McKechin, a member of the Commons Arms Export Committee, said: "I am deeply concerned that such a company is participating in this event. I believe the government should urgently consider revoking any relevant permission or licence and call on the organisers to cancel their conference place without delay."

However, Boris Johnson refused to weigh in against Rostec's presence at the arms show, saying: "Well, you know. It's very important that there should be access to legal weapons. As far as I understand it, there is no question of illegality and this is an argument that is of great antiquity.

"On the bright side, and I think that is what the Huffington Post should look at, it's also true that global conflicts are diminishing in number."

Despite the Mayor's reluctance to criticise the presence of Russia for its links to the Syrian regime, he recently branded the parliamentary vote against military intervention in Syria as a "great shame".

"It is a great, great shame that when somebody is killing large numbers of innocent people with gas, men, women and children, it is a great shame that a country like ours that stands for civilised and decent values around the world cannot do anything," he told Channel 4.

"I have to say, whatever your views about intervention, we should be able to assert our strong, strong revulsion and to make that clear to Assad."

Foreign Office minister Alistair Burt told MPs last Monday that the government regarded "respect for human rights" and "fundamental freedoms" as "mandatory considerations" in deciding how to invite to the DSEI fair.

"We review invitations in cases where the situation in any one country changes significantly prior to an exhibition," he added.

A spokesperson for the DSEI show said: "Any company that wishes to exhibit at DSEI must apply to the show organisers. This requires them to go through a robust compliance process to ensure that all equipment, services, documentation, and any other forms of promotion they wish to exhibit are compliant with UK, EU and international law.

"Ultimately, it is Government policy and the law that determines which companies can exhibit at DSEI and what they can exhibit."

"Those companies approved to exhibit at DSEI are subject to regular compliance checks throughout DSEI which are carried out by HMRC and staff from DSEI’s internal compliance team."

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