There has never been any need for customers to be concerned about security.

Barclays' spokesperson

Judge Stokes said: "On the defendant's own admission, he acted stupidly, irresponsibly and foolishly."

Outside court, Mr Browne's solicitor Jeffrey McCann said: "Mr Browne is tremendously relieved."

He said Mr Browne could not comment further because of a High Court order preventing him from discussing the matter.

Secret compartment

Sallie Bennett-Jenkins, prosecuting, said he had threatened to disclose coded keys which would have put the security of millions of credit and debit cards worldwide in jeopardy.

She said he had become "disillusioned, bitter and angry" with the bank before finally resigning from his job.

Mr Browne, from Cranage, near Holmes Chapel, Knutsford, had complained that his suggestions on improving security were not being taken up, and between March and September last year he sent four letters to Barclays' chief executive making the blackmail claims.

The court heard that when police searched his home they found items connecting him to the letters hidden in a secret compartment under his kitchen sink.

'Ludicrous'

In the letters, Mr Browne had demanded a team of experts named by him should be paid �1.7m each to devise better security measures.

He said it was done in a jokey way in order to bring the bank's attention to his fears about scrapping an internal security system.

The demands for �25 million were described by Mr Browne as "ludicrous", and he did not think the letters would be taken seriously.

'Fairly unstable'

He said: "I expected to be instantly found out and have people on my doorstep demanding an explanation for what I was up to and what I was trying to achieve."

He added that he felt his department had been under funded.

The refusal to accept voluntary redundancy, his step-father's death and the failure of his marriage meant he was "fairly unstable" by the time he resigned in January 2000.

After this his local branch had mistakenly emptied his account of �8,600, leaving him overdrawn.

The bank had apologised, sent him a couple of bottles of wine - then sent him the bill.

He thought that was fairly amusing until he got a �4 bill for the interest on the overdraft.

"That is what threw me over the edge," he said.

After the verdict a spokesperson for Barclays said: "There has never been any need for customers to be concerned about security.

"This case was brought by the Crown Prosecution Service and, as Barclays is not a party to the proceedings, it would be inappropriate for us to comment on the verdict."