Adults who commit the premeditated murder of a child will be given tougher sentences of life without parole under plans due to be included in the Conservative party’s manifesto.

Robert Buckland, the justice secretary, said it was his aim to stop the parents of murdered children seeing the “sickening” spectacle of their killers walking free.

He said a Conservative government would change the sentencing guidelines to advise that the premeditated murder of a child under 16 by an adult over 21 should be subject to a “whole life order”, so they would never be able to apply for release.

The current rules require the murder to be of multiple children or to be sexually or sadistically motivated.

The move is one of several policies on tougher sentencing as the Tories seek to make tackling crime a central election issue. This is despite it causing problems for the party in the 2017 election, when Theresa May was repeatedly challenged over her cuts to the police service while home secretary.

Buckland said: “There can be no more sickening injustice than that of heartbroken parents watching the killer of their child walk free.

“That’s why under a Conservative majority government, the law will be rewritten to be absolutely clear: any murderer who denies a young, innocent child the right to life surrenders their own right to liberty. They do so permanently, and they do so without exception.

“There is nothing we can do to take away the pain of the families of murdered children. So we must do everything in our power not to compound it.”

Buckland also announced plans to reduce reoffending – an aim of multiple governments in the past. He said a dedicated prison education service would oversee the education and skills training offered across all jails and prisoners would be offered more hours of work while in jail.

A former director general of the Prison Service, Sir Martin Narey, warned last month that rehabilitation of offenders in jail through short courses and training does not work to fix problems caused by difficult lives.

Narey advised: “Stop fretting about rehabilitation. Politely discourage those who will urge you to believe that they have a six-week to six-month course which can undo the damage of a lifetime.

“The next time someone tells you they have a quick scheme which can transform lives – ‘transform’ is the word of which you should be particularly suspicious – politely explain that life isn’t that simple.”