London, Aug 9 : Cyber attacks on British Government computer systems and vital parts of the economy have become one of the greatest threats to national security, an official report has disclosed.

The Government confirmed for the first time that a series of electronic assaults on official and private sector databases have already been carried out and are continuing.

Though the Cabinet Office report did not identify who carried out the ''well-resourced and sophisticated attacks'', Whitehall sources disclosed that China is suspected of state-sponsored espionage.

Beijing has issued furious denials that it was engaged in such practices and the timing of yesterday''s warning is particularly sensitive, coming on the opening day of the Olympics.

But intelligence officials fear there is clear evidence China is mounting an aggressive push to establish ''electronic dominance'' over its global rivals.

It would use cyber-warfare to cripple an enemy''s financial, military and communications capabilities in a conflict.

Chinese groups are also said to be using ''Trojan'' software to hack into the networks of firms and Government departments and access confidential data.

Jonathan Evans, director-general of MI5, has sent a letter to 300 chief executives and security chiefs at banks, accountants and legal firms warning them they are under attack from ''Chinese state organisations''.

Other countries - notably Russia - are thought to be using similar techniques.

“E-espionage” was identified by the Government as one of the two most likely risks facing the UK, the other being terror attacks on the transport network.

The Cabinet Office published its first annual risk register which highlighted the dangers posed to Britain''s security from other countries as well as terrorist groups, natural disasters and major accidents. (ANI)