Serious terrorists will be forced to serve their entire prison sentences without any prospect of early release as part of a crackdown announced on Tuesday.

All offenders convicted of preparing or committing a terrorist act will face a minimum of 14 years in jail, more than four times the present three years - and the current rule allowing release of serious terrorists two-thirds of the way through the sentence will be abolished.

They will also face tougher controls on release including lie detector tests that could help prevent a repeat of the London Bridge terror attack where killer Usman Khan is thought to have conned police and probation into thinking he had reformed.

The introduction of fixed-term sentences for terrorists will fuel demands for early release to be scrapped for offences across the criminal justice system so offenders serve the jail terms handed down by judges.

Boris Johnson is proposing longer sentences for serious violent and sex offenders by abolishing the current release at the half way point but they will still be eligible for parole two-thirds of the way through their jail terms.