The papers detail the activities of Patriarch Alexiy, who was code-named "Agent Drozdov" (the thrush), in actions against orthodox clergy and believers.

Patriarch Alexiy has been a strong supporter of President Putin, himself a former KGB agent, and has issued public statements defending Mr Putin's conduct of the war in Chechnya and his stance on the sinking of the nuclear submarine Kursk. He has consistently opposed all proposed visits to Russia by Pope John Paul II.

Under his patriarchate the church has received special privileges, including the right to import alcohol and tobacco at reduced rates of duty for sale in the Russian Federation.

There have been allegations against the Patriarch for some time but they have been consistently denied by the church. The most recent denial was made on Wednesday by a church spokesman, Father Vsevolod Chaplin, who said: "There are no data indicating that Patriarch Aleksiy II was an associate of the special services, and no classified documents bear his signature."

But the Keston Institute, an Anglican religious rights organisation, has informed The Irish Times that it has "reviewed all the available documentary evidence from the various archives of the KGB" and has concluded that the allegations are based on fact.

Representatives of the Keston Institute have had access to documents in Tallinn which reveal that the Patriarch was recruited by the Estonian KGB on February 28th, 1958. Although he is referred to only as "Drozdov" the documents make it clear that they refer to the then Father Alexiy Ridiger as the personal details given match those of no other priest of the Estonian diocese.

The document in the Estonian State Archive (record group 131, file 393, pages 125-126) signed by the chairman of the Estonian KGB, Col I.P.Karpov, and the head of the Fourth Department "Belyayev" notes that Drozdov "positively recommended himself" to the KGB.

It adds: "During secret rendezvous he was punctilious, energetic and convivial. He is well-oriented in theoretical questions of theology and the international situation. He has a willing attitude to the fulfillment of our tasks and has already provided materials deserving attention which are forming the basis for documentation of the criminal activity of a member of the leadership of the Johvi Orthodox church . . .

"In addition, `Drozdov' also provided valuable material for the case under way against the priest Povedsky. At present he is working on improving his knowledge of German. After consolidating the agent's experience in practical work with the organs of state security in the cultivation of agents, we intend also to use him in our interests by sending him to capitalist states as a member of church delegations."

KGB papers in the Moscow archive state that Drozdov was sent to England in 1969 as part of a church delegation, that he and another agent were involved in "educational work" with monks in Pskov in western Russian in March 1983 and that he was sent on a mission to Portugal in 1985.

According to Keston, a file in the archive dated February 1988 states: "An order of the USSR KGB chairman was prepared to award Agent Drozdov the Certificate of Honor."