The most senior judge in the country makes wide criticisms of the criminal justice system today and warns prison overcrowding is proving "absolutely fatal" for efforts to tackle the treatment of inmates.

The remarks by Lord Phillips, lord chief justice of England and Wales, are likely to put further pressure on the Home Office, which is reeling from the release of foreign prisoners. The prison population is predicted to pass 80,000 by autumn.

In a broad-ranging interview for the Guardian, his first on penal matters, Lord Phillips warns that judges should not send people to prison unless they really have to and that the "sensible place for rehabilitation is in the community".

He said one reason why prison numbers were rising was because drug users were deliberately committing offences to get on prison help programmes. "We need much better drug rehabilitation facilities in the community," he said."It should not be necessary to commit an offence in order to get drug treatment. I am afraid the reality in many parts of the country is that it is."

He also said:

• it was pointless to send people to jail for two-week sentences;
• there should be many more beds for prisoners with mental health problems so that they could be taken out of jails;
• that the public would not tolerate community sentencing if it did not involve "significant punishment";
• he had come across prisoners offered community sentences who preferred to go to prison, so they could get treatment.

His comments, some of which are at odds with the government's message on the use of prison, came after he visited Brixton prison last week and discussed problems with inmates and staff.

The Home Office said there were several alternatives to custody including "robust community sentences that can include a wide range of requirements, including unpaid work, drug treatment, and curfews".

"We believe that constructive community sentences can play an important role in reducing re-offending amongst less serious offenders, however imprisonment should continue to be used to protect the public from the most serious offenders - those who are violent, dangerous or seriously persistent."

Lord Phillips said that prison obviously worked as a punishment for dangerous offenders. But the "sensible place to carry out rehabilitation" was in the community.

Prison was not the place to treat people with serious mental health problems, but, as there were currently not enough places in hospitals to treat them, they remained in jail for months. There was a temptation for courts to send someone to jail for "a touch of prison", but this made life "impossible" for people trying to run jails.

Lord Phillips' visit to Brixton was arranged by members of the Independent Monitoring Board and the prison' s governor. Angela Clay, chair of the Association of Members of Independent Monitoring Boards, said care in the community was failing many vulnerable people. "Nobody will take responsibility for these people as they revolve between prison and the fractured life they lead outside," she said. "The circle has to be broken."

Juliet Lyons, of the Prison Reform Trust, said that the prison system was facing its worst crisis for 15 years. "Prisoners and prison staff are standing in the wreckage of a system treated like a political football by all those determined to talk tough on crime."