Hundreds of post office workers have won a key victory against the Post Office and the controversial accounting software they were forced to use

It is the first step towards overturning the convictions of postmasters accused of fraud or theft after using the Horizon IT system.

Their lawyer said they could "now walk with their heads held high" after the ruling which ends years of campaigning.

It comes after the Post Office had said it would pay £58m to settle claims.

Last week the Post Office had acknowledged problems with the IT system but Monday's judgment has been made as part of a court case launched before that settlement was reached.

In the case, brought by six lead claimants, the judge looked at allegation that the system contained a large number of software defects, which caused shortfalls with sub-postmasters and postmistresses' accounts.

In Monday's High Court judgment, Mr Justice Fraser said the Horizon IT system was not "remotely robust" and even when improved it had a significant number of bugs.

He said there was a "material risk" that shortfalls in Post Office branch accounts were caused by the system.

The Post Office workers blame the system for creating big shortfalls in their accounts, discrepancies which led to some being made bankrupt and others prosecuted and sent to prison.

Homes, businesses and reputations have been lost, as well as years spent in prison.

Among those involved in the case is Seema Misra, who was pregnant with her second child when she was convicted of theft and sent to jail in 2010.

She was accused of theft after using the Post Office Horizon IT system, which is provided by Fujitsu.

Seema became a sub-postmistress in West Byfleet in Surrey in June 2005 and was suspended in January 2008 after an audit found a discrepancy of £74,000 in her accounts.

She had been feeding at least £100 per day from her shop into the Post Office tills, because of discrepancies in balancing the accounts. One day there was a £10,000 hole.

SOURCE:BBC