Prison reform charities have condemned the government’s enthusiasm for extending minimum prison terms as “the politics of the lynch mob” and an unnecessary duplication of existing judicial powers.

Proposals in the Queen’s speech to ensure violent and sexual offenders serve a minimum of two-thirds of their sentence – compared with half under current guidelines – before becoming eligible for release on licence have attracted widespread criticism.

Frances Crook, the chief executive of the Howard League for Penal Reform, said: “This is not a sensible, evidence-based policy; it is the politics of the lynch mob. This is about making people spend more time in prison, which will affect thousands of men and will probably put staff in danger by taking hope away from people.

“We already know that prisoners are in appalling conditions, with a lot of violence, injury and suicides. A lot of it is directed at staff. This is very irresponsible.”

The Prison Reform Trust pointed out: “Judges can already hand down two-thirds sentences in certain cases, for example if it’s one of 100 specific offences or if the person poses a risk to the public.”

Chris Daw QC, a criminal and fraud expert, tweeted: “Make no mistake, the current Tory approach to crime and punishment is just dangerous, populist electioneering. Nowhere in the free world do longer and longer prison sentences do anything good for society.”

77 more courts in England and Wales to close Read more

The government’s emphasis on ramping up punishments was contrasted by many commentators with its failure to pay for judges to hear backlogs of cases and the protracted underfunding of the justice system.

Richard Atkins QC, the chair of the Bar Council, which represents barristers across England and Wales, said the Queen’s speech “acknowledged that public confidence needs to be restored in the criminal justice system. I hope that this is an acceptance of what we have long warned, that our criminal justice system can bear no more.

“For the last decade, the Ministry of Justice has been in dire need of rescue as it has buckled under the strain of greater budget cuts than any other Whitehall department – 40% since 2010.”

Louise Haigh, Labour’s shadow policing minister, was more dismissive, tweeting: “Many of the criminal justice #QueensSpeech measures had already been announced by May’s Govt. The 20,000 officers we already know won’t be going to the frontline. No new ideas, not enough new cops and no acknowledgement that austerity has destroyed the criminal justice system.”

The Criminal Bar Association (CBA), which represents English and Welsh barristers working in the criminal courts, highlighted the fact that many suspects in serious crimes were being released under investigation, without being subjected to bail restrictions.

Caroline Goodwin QC, the CBA chair, said: “Fewer prosecutions does not mean less crime is being committed – quite the reverse. More crimes are being reported and yet fewer are being prosecuted.

“At present, the rate of 7.8% of all crimes reported to police resulting in a charge or summons is simply unacceptable. Exactly how is the general public to have faith in our criminal justice system? That rate has broadly halved in under a decade.”

The Law Society, representing solicitors in England and Wales, said it was concerned by government proposals for weakening the Ministry of Defence’s legal and public accountability.

The society’s vice-president, David Greene, said: “The UK upholds and respects the rule of law on and off the battlefield across the world. The rule of law dictates that everyone should be held accountable within our framework of laws. It must not matter how the accused or defendant may be perceived by the public, media or government.”