Nearly 40 Russian spies are thought to be involved in different types of espionage activity in Britain, according to a recent report by the Telegraph.
Their activities include both traditional intelligence gathering as well as industrial spying such as accessing trade and business secrets.
The UK security agencies are expecting a spike in the activities of the Russian diplomats, who are engaged in espionage activities due to two big upcoming events in the country, the Olympics Games and the Queen's Diamond Jubilee celebrations.
During summer, the UK intelligence officers would be concentrating more on these big events.
The newspaper report also indicated that the close relationship between the UK and the US is one of the reasons for the Russian interest in Britain. Russia would be trying to get backdoor access to US intelligence through its spies in Britain.
According to the Telegraph, the number of Russian spies in Britain today almost matches the number during the cold war era.
Here is a look at top five intelligence agencies around the world:
1. Central Intelligence Agency (CIA), US
The Central Intelligence Agency (CIA) is responsible for providing national security intelligence to senior US policymakers. The CIA gathers intelligence through non-military, commissioned civilian agents, trained to avoid tactical situations.
The Washington-headquartered agency is also reported to be engaging in tactical operations occasionally. The agency is headed by David Petraeus.
The CIA is widely believed to be behind the Abbottabad operations last year in which al-Qaida chief Osama Bin Laden was eliminated.
2. SVR, Russia
The Russian Foreign Intelligence Service or SVR is Russia's external intelligence agency, and is the successor to the First Chief Directorate (PGU) of the KGB since December 1991.
With its headquarters in Yasenevo District of Moscow, the SVR is responsible for intelligence and espionage activities outside the Russian Federation.
It works in cooperation with the Main Intelligence Directorate (GRU), which also reportedly deployed many agents in foreign countries.
The SVR is authorised to negotiate anti-terrorist cooperation and intelligence-sharing arrangements with foreign intelligence agencies, and provides intelligence to top policy makers in Russia.
3. MI6, UK
MI6 is the British intelligence agency responsible for protecting the United Kingdom against overseas threats.
The MI6 was formed in 1909 and is headquartered in Vauxhall Cross, London. It is responsible for collection, analysis and appropriate dissemination of foreign intelligence. The agency is headed by Sir John Sawers KCMG.
MI5 deals with domestic security and counter intelligence service of the UK.
It has eight regional offices around the UK and a Northern Ireland headquarters.
The Service is organised into seven branches, each with specific areas of responsibility to counter threats including terrorism, espionage and the proliferation of weapons of mass destruction.
The agency is currently headed by Director General Jonathan Evans, and based at Thames House, London.
4. Mossad, Israel
The Institute for Intelligence and Special Operations, widely known as Mossad, is Israel's official intelligence agency, which is also used to perform special covert operations beyond its borders.
A look at Mossad's Web Site reveals that it engages in covert intelligence gathering beyond Israel's borders, preventing the development and procurement of non-conventional weapons by hostile countries and preventing terrorist acts against Israeli targets abroad.
It also produces strategic, political and operational intelligence for the country.
Based in Tel Aviv, the agency is headed by Tamir Pardo.
5. DGSE, France
The General Directorate for External Security (Direction Générale de la Sécurité Extérieure, or DGSE) is France's external intelligence agency. Operating under the French ministry of defence, the agency works alongside the DCRI (the Central Directorate of Interior Intelligence) in providing intelligence and national security, by performing paramilitary and counterintelligence operations abroad.
As with most other intelligence agencies, details of its operations and organisation are not made public. The DGSE claims to have prevented more than 15 terrorist attacks in France since 9/11.
Formed in 1982 and based in Paris, the agency is headed by its Director Erard Corbin de Mangoux.