Usman Khan, 28, (pictured) was one of at least 350 convicted or suspected terrorists to be freed since 2012

One in seven Islamist extremists jailed for terrorism have had their sentences cut on appeal.

They include fanatics who plotted to blow up shopping centres, nightclubs and Army bases. Others targeted members of the Royal Family and led Al Qaeda cells planning murder on a 'colossal scale'.

Many returned to making calls for jihad and radicalising recruits almost the moment they left jail and later had to be locked up again.

The figures come in the wake of the London Bridge knife murders by an extremist released halfway through a 16-year sentence.

Usman Khan, 28, was one of at least 350 convicted or suspected terrorists to be freed since 2012. Campaigners said 'woolly liberal judges' were putting public safety at risk.

Forty of the 264 fanatics convicted of Islamist-inspired terrorism between 1998 and 2015 managed to have their sentences reduced on appeal, according to the Henry Jackson Society.

At least seven have been jailed again since their release or had to return to prison for breaking licence conditions, including some caught spreading hate online or trying to travel to join Islamic State.

Left: Shah Jalal Hussain had his 2008 sentence for fundraising for terrorism in Iraq and breaching bail reduced by nine months. Right: Dhiren Barot was sentenced to a minimum of 40 years in 2006 after researching how to commit murder on a 'colossal and unprecedented scale'. His sentence was later cut to 30 years

They include Ibrahim Abdullah Hassan, a member of the now banned group Al-Muhajiroun, who had his sentence for inciting terrorism reduced by nine months despite calling for Tony Blair's assassination.

He resumed associating with Al-Muhajiroun as soon as he left prison and was locked up again for three years for encouraging terrorism online.

Omar Brooks, a former spokesman for the group, had his sentence of four years and six months cut by 12 months following his 2008 conviction for defending the beheading of British hostages in Iraq and preaching: 'We are terrorists – terrify the enemies of Allah.'

Left: Abu Izzadeen. Right: Ibrahim Abdullah Hassan, a member of the now banned group Al-Muhajiroun, had his sentence for inciting terrorism reduced by nine months despite calling for Tony Blair's assassination

As he walked out of Pentonville Prison in October 2010 he addressed supporters, accusing UK troops in Afghanistan of torture, rape and killing. Brooks has since been jailed twice, once in 2015 for failing to notify the police of a change of address as required and in 2016 on suspicion of trying to reach Syria.

Neighbours in dark over fanatics next door The number of Islamic State fighters and their families who have returned to Britain is being kept secret by Labour councils. The locations where they now live are also being kept under wraps to protect the jihadis. Three councils said tensions could be inflamed if residents learnt IS families have settled in their town. The Mail asked 150 councils how many children had returned from IS-controlled Syria, whether they had come back with their parents and if they had been taken into care. The majority said they could not collate figures. But Labour councils Oldham, Lewisham in south London, and Coventry used a loophole in freedom of information laws to neither confirm or deny. Oldham council said confirming 'would create a risk of heightening community tensions'. And Coventry council said: 'Knowledge that Syria returnees live in an area may trigger an increase in offences, for example, hate crimes.' Philip Davies, Tory candidate for Shipley, West Yorkshire, said: 'Returning jihadi should not be given special treatment.' Advertisement

Another extremist, Shah Jalal Hussain, had his 2008 sentence for fundraising for terrorism in Iraq and breaching bail reduced by nine months. In 2014 he was jailed a second time for encouraging terrorism and spreading terrorist propaganda online.

Khan, the killer of two Cambridge graduates at London Bridge last month, was released from Woodhill Prison in Buckinghamshire last Christmas Eve. In 2012 he was handed an indeterminate sentence for public protection, with a minimum term of eight years – meaning he could have been kept in prison for as long he was deemed to be a public threat.

But in 2013 Lord Justice Leveson granted an appeal and his sentence was replaced with a 16-year fixed term with at least half spent in jail.

He was originally convicted over a plot to bomb the London Stock Exchange.

Dr Rakib Ehsan of the Henry Jackson Society, a security think-tank, said: 'Lord Justice Leveson's disastrous decision to slash London Bridge terrorist Usman Khan's sentence was far from an outlier. For too long, woolly liberal judges have failed to take robust enough action over Islamic extremism.'

Boris Johnson has said it is 'repulsive' that someone as dangerous as Khan could be released after only eight years.

A Conservative Party spokesman said: 'This is exactly why the PM called for changes in August to our sentencing regime but this was stalled because of the gridlock in parliament.

'If we get a working majority we will change the law to ensure serious terrorists serve at least a 14-year term and every day of the sentence they are handed down. Unfortunately Jeremy Corbyn has said that he does not think terrorists should 'necessarily' serve a full sentence.'

Dhiren Barot was sentenced to a minimum of 40 years in 2006 after researching how to commit murder on a 'colossal and unprecedented scale'. His sentence was later cut to 30 years.