China's People's Liberation Army is conducting a concerted campaign of cyber espionage against UK businesses, the head of MI5 is warning.

Spy chief Jonathan Evans has written to financial, legal and retail firms this morning to warn of the threat and advise companies to undertake a risk assessment of their IT security defences, according to consultancy KPMG.

The letter, which was received by financial, legal, and retail firms this morning warns that companies should do a risk assessment of their IT security defences.

"The Centre for the Protection of National Infrastructure (CPNI) has been monitoring activity from the People's Liberation Army in China," said KPMG principal advisor Martin Jordan, who has seen a copy of the letter.

"The activity has led them to believe that there is a serious and concerted attempt at electronic espionage through every sinew of British industry."

Chinese companies are allegedly looking to make financial gain out of the information.

"If they know that British firms are trying to buy a company or a plot of land in China then they have got room to manoeuvre at the negotiating table because they know what a company is prepared to pay," said Jordan.

Last summer a slew of cyber attacks on Whitehall departments were alleged to have originated in China. Beijing strenuously denied the claim .