Opposition politicians have criticised a government overhaul of official sentencing guidelines.

Under plans detailed in the Management of Offenders and Sentencing Bill, prison sentences are to be linked to whether there are enough places in jail.

Judges will consider the number of people in prison when deciding if a criminal should be jailed or given an alternative community sentence.

Shadow home secretary David Davis slammed the plans.

"For the first time in British history, sentencing will be decided by economics rather than the merit of an individual case," he said.

"It is a disgraceful violation of our criminal justice system and will lead to thousands of criminals getting shorter sentences, or no sentence at all, because the government has failed to provide enough prison places."

The legislation also includes plans for a huge increase in the maximum fines magistrates can impose.

And, controversially, the size of the fine would be linked to the income of the offender.

Minor offences that would currently carry a maximum fine of £200 would in future attract a penalty of £750 for those on high incomes.

Liberal Democrat home affairs spokesman Mark Oaten argued that the new system "runs the risk of producing  crazy fines which would undermine public confidence in the system".

"Local judges and magistrates already have the power to set fines and can take people's income into account when deciding the level of a fine," he said.

"It's better to decide the level of fines on a case by case basis than have a central system that could create a great sense of unfairness."