Glitter, 78, whose real name is Paul Gadd, was sentenced in 2015 for attempted rape, four counts of indecent assault and one of having sex with a girl under 13.

He was one of the biggest music stars of the 1970s.

A justice ministry spokesperson told the BBC Gadd will be closely monitored by probation officers.

The BBC understands he will be fitted with a GPS tag.

Gadd had been at the height of his fame when he attacked two girls aged 12 and 13 after inviting them backstage to his dressing room.

His youngest victim had been less than 10 years old when he crept into her bed and tried to rape her in 1975.

Gadd had been held at HMP The Verne - a low security category C jail in Portland, Dorset. Having received a fixed-term sentence, he was automatically freed halfway through his term.

A Ministry of Justice spokesperson told the BBC that "sex offenders like Paul Gadd are closely monitored" by the police and probation officers, and "face some of the strictest licence conditions".

"If the offender breaches these conditions at any point, they can go back behind bars," the spokesperson said.

Gadd will not be added to the sex offenders' register for these crimes, because they were committed before the registry was introduced. However, he was already ordered to sign the register for life when he returned to the UK after he was found guilty of sexually abusing two young girls in Vietnam in 2006.

At the time of sentencing in 2015, Judge Alistair McCreath said he could find "no real evidence that" Gadd had atoned for his crimes.

He described Gadd's abuse of a girl under 10 as "appalling" and said: "It is difficult to overstate the depravity of this dreadful behaviour."

"You did all of them real and lasting damage and you did so for no other reason than to obtain sexual gratification for yourself of a wholly improper kind," Judge McCreath said.

Gadd had denied allegations against him but was found guilty after a trial lasting three weeks.

Sex offenders are subject to conditions including:

* Being made to attend meetings with a probation officer, who they must tell if they change their name

* Needing to request permission before travelling abroad - some offenders may face stricter overseas travel restrictions

* Having to provide police with personal details, including an address, which is updated annually and whenever details change

* They can also be prevented from unsupervised contact with children and face restrictions on internet use

* They can be immediately returned to prison if they breach the conditions

The allegations that led to Gadd's imprisonment came to light when he became the first person to be arrested under Operation Yewtree - the investigation launched by the Met in 2012 in the wake of the Jimmy Savile scandal.

Det Ch Insp Michael Orchard, from Operation Yewtree, said Gadd was a "habitual sexual predator who took advantage of the star status afforded to him".

Gadd, performing as Gary Glitter, was one of the UK's biggest glam rock stars of the 1970s, with three UK number ones, including I'm the Leader of the Gang (I am!).

His fall from grace occurred decades later, after he admitted possessing thousands of images that showed child sex abuse and was jailed for four months in 1999.

After being freed he went abroad, and in 2002 was expelled from Cambodia amid reports of sex crime allegations. In March 2006 he was convicted of sexually abusing two young girls in neighbouring Vietnam and spent two-and-a-half years in jail.

Gadd, who stood accused of kissing, fondling and engaging in other sexual acts with the girls, evaded more serious charges of child rape, which carried a maximum penalty of death by firing squad.

On his return to the UK in 2008, the former pop star was ordered to sign the sex offenders register.

In 2012, he was arrested at his London home following an investigation by detectives from Operation Yewtree, before the case that led to his latest conviction came to trial in January 2015.