The government's crime "crackdown" is set to trigger crisis levels in the prison population, it was claimed on Friday.

With jail numbers soaring by 600 prisoners a week, the prison system is set to reach its capacity of 71,000 within weeks.

Figures showing the prson population to have hit the 69, 689 mark, have prompted calls for magistrates to be stripped of their powers to mete out custodial sentences.

Prison Service chief, Martin Narey, has described the soaring prison population as "utterly inexplicable".

"Things are very tight at the moment. For the last three weeks there has been an utterly inexplicable rise in the prison population of about 600 prisoners a week. And that in a period during which the Home Office statisticians told us there would be no rise in the population at all," said Narey.

"That's put us under very severe strain. The home secretary said since July that he wants short sentenced prisoners who don't need to be locked up being sentenced to the community. The lord chief justice has said it and I've said it. But still we're getting this very, very significant increase in the use of custody and it is putting us under considerable strain."

It is predicted that the UK's prison population is set to rise as high as 83,500 within the decade - an increase that would put the UK second in the world's league table.

Mike Newell, the president of the Prison Governors' Association, has urged unprecedented action to cut numbers by stripping magistrates of powers to jail convicts.

"Magistrates now have a wide range of community penalties available to them but they insist on imposing inappropriate prison sentences," he said.

"We say these powers should now be taken away from them to stop such inappropriate sentencing."

Magistrates can only jail people for a maximum of 12 months, but Newell believes short sentences "often cause more harm than good".

"We have worked out that there are 4,000 people serving sentences of a week or less. Clearly these sort of sentences are not appropriate," he said.

"If these people had not been sent to prison, the pressure on the system would not be so great. Only this week a 77-year-old man was jailed for seven days for not filling in his census form properly. That cannot be right. If magistrates are not going to use their powers properly they should be stripped of them."

The Howard League for Prison Reform has called on David Blunkett to take immediate action.

It blames the "tough on crime" political agenda for the rise in prison's number.

"The government must stop pretending that locking up ever increasing numbers people protects the general public from crime," said the charity's director, Frances Crook.

"Instead the home secretary should be honest and admit that taxpayers' money would be better spent on schools and hospitals than yet more prisons and that crime would be more effectively tackled by focusing on some of the most effective restorative and community based sentences."