MIA: Encyclopedia of Marxism: Glossary of Organisations
All-Russian Central Executive Committee
A body elected by the Congress of Soviets, the first Central Executive Committee was elected at the first All-Russian Congress of Soviets in Petrograd, June 3 - 24, 1917. After the October revolution, the Second All-Russian Congress of Soviets met, and elected the second Central Executive Committee which was the executive body of the R.S.F.S.R., and was compromised of:
The Committee had 100 members and a chairman, the later of who directed the day to day work of the Committee and only voted in the case of a even split in the committee. The first chairman of the CEC was Leon Kamenev.
All Russian Co-operative Society
The All-Russian Co-operative Society (ARCOS) was the principal body responsible for the orchestration of Anglo-Russian trade in the early days of Soviet Russia, following the development of Lenin's New Economic Policy. In 1927 the organisation was raided by British authorities, who accused the company as serving as a front for subversive activities.
The All-Russian Co-operative Society, Ltd., began operations in London in October 1920. The name "Arcos" is actually an acronym deriving from the formal name of the company: All-Russian Co-Operative Society, although in the contemporary press the name was typically capitalised as would be a proper name (i.e. "Arcos").
Arcos was established as the official buying and selling agency of the Soviet government in the United Kingdom. Arcos was a British company, operating under British law, although the stockholders were all Soviet citizens.
Arcos made £1,970,000 worth of purchases during calendar 1920, with payment for its purchases made in gold via Reval. The company bought an additional £3,650,000 worth of products during the first 8 months of 1921. Chief among its purchases were food, textiles, and coal, although a rather limited quantity of agricultural machinery was also obtained. The company was also the conduit for the sale of over £300,000 worth of Russian produce up to August 1921, primarily flax, but also including timber, manganese, and furs.
The suspicions of Mi5 that Arcos was acting as a front organisation for espionage activity were first aroused in 1925 when John Ottaway had tailed a suspect back to the Moorgate offices.  The suspect Ottaway was following, Walter Dale, then went to the offices of the Federated Press of America, which served as a journalistic cover for left wing espionage in the UK. Mi5 tapped the phonelines of the FPA which revealed a raft of calls not only to Arcos but also suspected Soviet intelligence operatives, whilst interception of its post revealed copies of classified French dispatches. 
The Arcos Affair of 1927
On 31 March 1927 SIS passed evidence to Mi5, courtesy of an informant inside Arcos, that Arcos had illegally procured and copied a classified Signals Training manual from the Aldershot military base.  The British secret service also had testimony that the basement of 49 Moorgate contained photostat apparatus, for the purpose of photographing stolen secret documents.
At 4:20 in the afternoon of 12 May 1927, a large force of uniformed and plain-clothes police officers entered the headquarters of Arcos and the Soviet Trade Delegation, located at 49 Moorgate in London. The police took possession of the telephone exchange, detained all employees, and made a thorough search of documents on the premises. Drilling machinery was brought in to open locked rooms and strongboxes. They immediately proceeded to the basement they had been tipped off about, recovered numerous classified documents, found it to be rigged with numerous anti-intruder devices and notices forbidding entry, for which the employees had no satisfactory explanation. 
A secret cypher room was discovered, that had no door handle and could only be entered with a key, wherein workers were hurriedly engaged in burning papers. A struggle then ensued when Police tried to arrest remaining papers from staff. The chief of this room then attempted to pocket a list, which on inspection detailed cover addresses used for secret communication with the communist parties of the North and South American, African and Australasian continents. 
A considerable number of documents were removed from the building in the course of the investigation. This raid and subsequent diplomatic fisticuffs subsequently became known as the Arcos Affair.
The next day, the Soviet Embassy handed in an official note of protest, stressing the illegality of the raid on Arcos headquarters. It was noted by the Soviet government that the Chairman of the Trade Delegation, Mr. Khinchuk, was protected by diplomatic immunity in accord with the Anglo-Russian Trade Agreement of March 16, 1921.
The Conservative Baldwin government accused the USSR of using the organisation for the conduct of "military espionage and subversive activities throughout the British Empire and North and South America." Diplomatic relations and trade agreements between the USSR and Britain were abruptly dissolved shortly after the incident and a war scare swept the Soviet Union.
Despite the highly-publicized raid of Arcos and the manpower and time put into the operation, little of practical import resulted from the raid. Historian Louis Fischer noted of the Arcos raid:
"It disclosed nothing that had not been known before, and failed to produce the highly important War Office documents the rumored theft of which served as excuse for the raid. The official White Paper containing the documents found in the raid was thin evidence indeed, and led to no arrests or charges for illegal or subversive activities by Russian or British subjects."
During its six years of existence, Arcos did approximately £100,000,000 in trade between Britain and Soviet Russia.
Aftermath of the Arcos raid
The government of Great Britain severed diplomatic relations with the USSR during the second half of May 1927.
In an attempt to provide justification for the raid on Arcos, Prime Minister Stanley Baldwin read aloud in the House of Commons from a handful of deciphered telegrams that proved Soviet guilt of espionage.  As a result of this the Soviets, now aware that the British secret services had been intercepting their communications, changed their encryption cyphers for all diplomatic communication. They adopted the virtually unbreakable one-time-pad system, therefore eliminating the ability of the British GC&CS to decipher any high grade Soviet messages from 1927 until the end of the Second World War.  Footnotes
1. "The Work of Arcos," Russian Information and Review, vol. 1, no. 1 (1 Oct. 1921), pg. 19.
2. "The Work of Arcos," pg. 19.
Louis Fischer, The Soviets in World Affairs. In Two Volumes. Princeton, NJ: Princeton University Press, 1951. Vol. 2, pg. 687.
3. "The Work of Arcos," pg. 19.
4. "The Work of Arcos," pg. 19.
5. "The Work of Arcos," pg. 19.
6. Christopher Andrew, "Defence of the Realm: The Authorized History of Mi5"(London, 2009), pp. 152-153.
7. Christopher Andrew, "Defence of the Realm: The Authorized History of Mi5"(London, 2009), p. 153.
8. Christopher Andrew, "Defence of the Realm: The Authorized History of Mi5"(London, 2009), p. 154.
9. The National Archives, Kew, file no.KV3/15.
10. Fischer, The Soviets in World Affairs, pp. 686-687.
11. The National Archives, Kew, file no.KV3/15.
12. The National Archives, Kew, file no.KV3/15.
13. Fischer, The Soviets in World Affairs, vol. 2, pg. 687.
14. Fischer, The Soviets in World Affairs, vol. 2, pg. 688. Fischer cites British White Paper, Russia No. 2 (1927): Documents Illustrating the Hostile Activities of the Soviet Government and the Third International against Great Britain. London: HM Stationary Office, 15. 1927.
16. Fischer, The Soviets in World Affairs, vol. 2, pg. 687.
17. Christopher Andrew, "Defence of the Realm: The Authorized History of Mi5"(London, 2009), p. 155.
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All-Russian Congress of Soviets
Each All-Russian Congress consisted from 650 to 2,000 delegates from Soviets all over Russia. Delegates were elected by the soviet of the local area they came: two deputies were chosen from each soviet with 25,000 to 50,000 electors, for every additional 25,000 electors an extra deputy was allowed, up to a maximum of eight deputies from a single soviet. Soviets with less than 25,000 electors were to combine with other soviets and send joint deputies to the Congress.
The executive power of the Congress of Soviets lasted several years after the October revolution in practice. In the late 1920s the Congress was seen as potentially counter-revolutionary. To ensure that it was not, the local leaders of the "Communist" Party nominated and elected the members of the Soviets to the Congress.
For an Event listing of the different Congresses of Soviets, see the Glossary of Events: All-Russian Congress of Soviets