Thousands of former offenders in the capital, including burglars and thieves, will no longer have to declare their criminal convictions in a move intended to boost their job prospects, ministers said today.

Under reforms that come into force next month, freed prisoners who were sentenced to six months or less will have to include their criminal history on application forms for only two years, instead of seven as at present.

More serious offenders will also see a dramatic cut in the length of time they are required to declare their convictions. It means thousands of former convicts who would previously have had to reveal their background when seeking work will be able to apply with a clean record instead.

Critics are likely to argue it could prevent employers from gaining an accurate picture of prospective staff.

But justice minister Simon Hughes said the change would be a vital support for people who want to turn their back on crime and rebuild their lives.

“This is the biggest change to the Rehabilitation of Offenders Act since the current system began in the Seventies,” he said.

“The aim is to ensure that people who made a mistake early in life are not punished indefinitely and are given the chance to contribute to society by getting an honest job and putting their offending behind them.

“We all pay a lot of money to keep offenders in prison and a lot of money if they they’re then on the dole and not paying taxes. So it’s in everyone’s interest to help people who have proved they can go clean.

“I think this change will mean the number of people who get back into work will significantly improve.”

Offenders sentenced to between six and 30 months will see the period during which they must declare their conviction fall from 10 to four years. Those jailed for between 30 months and four years, who were previously required to disclose the offence throughout their lifetime, will now only have to reveal it for seven years. Offenders given non-custodial sentences will also see the disclosure period reduced.

Mr Hughes, the Liberal Democrat MP for Bermondsey and Old Southwark, said safeguards would still exist for the most serious and dangerous offenders. Any convict applying to work in a school, hospital or other place containing “vulnerable” people will have to disclose their crime.

The convictions of those jailed for more than four years will never become spent — these will have to be declared whenever they apply for work.

Mr Hughes said it struck a balance between public protection and giving a “fair chance” to those who want to abandon crime.

Research has shown convicts who gain work are less likely to reoffend. In, 2012 a total of 91,000 offenders received a sentence of four years or less. Each will benefit from the reforms.

Under the new system, the number of years during which offenders will have to declare their convictions will begin from the end of their sentence, rather than the beginning as at present. That means that a criminal jailed for two and a half years will now have to disclose their conviction for a further four years after their release. making it a total of six and a half years since the start of their sentence.

That is significantly shorter than under the existing system which would require such an offender to declare their offence for ten years from the moment their sentence begins.