Disgraced broadcaster Stuart Hall would have received a "considerably greater" sentence than the two-and-half-years imposed today if he had been prosecuted under current laws, a court has heard.
His trial judge, Mr Justice Turner, said "the hands of this court are tied" as he explained his sentence was limited to the two-year maximum tariff at the time Hall indecently assaulted an underage girl.
He said that if the offences had been committed recently they would be classed as assault by penetration and sexual activity with a child - the former, in Hall's circumstances, would have led to a minimum eight-year jail term.
The ex-It's A Knockout presenter was cleared last week of 15 counts of rape in relation to two women who claimed they were sexually assaulted by him between 1976 and 1981.
The 84-year-old was convicted by the jury at Preston Crown Court of indecently assaulting one of the complainants when she was under the age of 16, and had earlier pleaded guilty to another indecent assault on the same girl when she was 13.
The charge Hall admitted involved an incident at a dinner party where he crept into the bedroom of his victim, known as Girl B, and assaulted her.
The married father-of-two is currently serving a 30-month jail term after he pleaded guilty last year to indecently assaulting 13 other young girls, aged between nine and 17, over a 20-year period.
The ex-BBC Radio 5 Live football match commentator had not been due for release from that custodial sentence until September.
Today's sentence will run consecutively from that date and means Hall will be a free man by December 2015 at the latest as he serves up to half his new sentence in custody before his release on licence.
Mr Justice Turner said: "The sentence for each offence has to be limited to the maximum sentence at the date when the offence was committed.
"This, therefore, is a ceiling beyond which this court is not permitted to go.
"It is a long-standing principle both of the English common law and under Article 7 of the European Convention on Human Rights that no-one may be punished more severely for an offence than the extent to which he or she could have been punished under the law that prevailed at the time the offence was committed.
"In that regard, therefore, the hands of this court are tied."
The prosecution brought charges of rape and indecent assault against Hall under the Sexual Offences Act 1956, which applied at the time the offences were said to have taken place.
But the jury heard it could not bring allegations - under the same act - of unlawful sexual intercourse with a girl under 16 because of a 12-month limit to when a complaint could be made after the offence. Hall's defence was largely that he had sex with the girls but it was consensual and he was not a rapist.
The indecent assault at the dinner party happened on the same occasion that he abused her friend in a bathroom - which he also admitted in the first court case.
He took advantage of the victims when they were sick after drinking from a bottle of spirits, the court heard.
Addressing Hall, Mr Justice Turner said: "You volunteered to help clean them up. Your real intentions, however, were far darker.
"You saw their condition not as a cause for concern but as an ideal opportunity to carry out acts of gross sexual molestation on the two girls while they were at least partly incapacitated by drink."
He went on: "It is difficult to resist the conclusion that it must have been with a sense of arrogant and contemptible immunity that you defiled each of these young girls, one in the immediate wake of another. It was an act of vile bravado and horrible betrayal."
The judge said if he had committed the offence on Girl B in more recent years the "definitive guideline" to Hall's conduct "would have been that relation to assault by penetration, the appropriate sentence for which would have been considerably greater than this court can accommodate".
Hall today received a sentence of 12 months for the offence.
The second indecent assault involved an act of oral sex which occurred within the context of the pair having "frequent" sexual intercourse at the BBC studios at Piccadilly and Oxford Road in Manchester, at a flat in Sale and on one occasion at a flat in central Manchester.
Mr Justice Turner said the jury was sure that oral sex had taken place on one occasion at least.
He said the "curious legal position" under the Sexual Offences Act 1956 was that the victim could not consent to indecent assault under the age of 16 but could consent to sexual intercourse.
He said: "The anomalous result is that, under the 1956 Act, the lesser offence of indecent assault can be charged at any time whereas the more serious offence of unlawful sexual intercourse is subject to a limitation period of one year."
The judge said the aggravating features of this indecent assault included "a gross breach of trust" in that he had known his victim for many years and she was entrusted in his care.
There was also an element of grooming involving flattery and the disinhibiting effects of alcohol, he said.
Mr Justice Turner said this assault would be today categorised as sexual activity with a child, which also "would have comfortably exceeded" the maximum sentence he could impose. Hall was sentenced today to 18 months for that offence, to run consecutively to the first indecent assault.
Hall, wearing a dark suit, white shirt and striped tie, was excused from standing as sentence was passed.
He sat impassively in the dock, with his head bowed, his legs crossed and his hands resting on his lap as he listened to the proceedings through a large pair of headphones.
The victim of his latest offences sat yards away in the public gallery and began wiping away tears with a handkerchief passed to her.
Her victim impact statement was not read out but the court heard Hall's offending had had "a profound effect" upon her.
Earlier, Crispin Aylett QC, in mitigation, said Hall was a man in his 80s who had been brought to account for offences committed more than 30 years ago and had now faced three separate sets of proceedings - his first lot of convictions, the Court of Appeal hearing to increase his sentence and his trial.
Mr Aylett said: "That would have been intolerable for anyone but for a man of 84, facing the prospect of dying in prison, the burden can scarcely be imagined.
"It is the third time in 18 months I have said on his behalf, he's been punished, he's been disgraced and for what it's worth, he's been financially ruined and I say on his behalf, enough is enough."
Hall, from Wilmslow, Cheshire, did not give evidence at his trial but his defence team did not dispute that he had sexual intercourse with both complainants.
Apart from one occasion when Hall said an alleged rape of one of the girls when she was aged 12 did not take place, his counsel argued the intercourse - when they were were in their mid-teens and he was in his mid-40s - was consensual and that he was not a rapist.
Many of the encounters were at BBC television studios in Manchester where Hall presented the corporation's regional news programme.
Both girls and their families were known to the defendant.
Last June, he was jailed for 15 months but the Court of Appeal ruled the sentence was "inadequate" and it was doubled a month later.
The appeal judges were told that Hall was "not in particularly robust health" and could die in prison.
He was stripped of his OBE for broadcasting and charity in the wake of his convictions.
An investigation into Hall's conduct has been carried out by retired High Court judge Dame Linda Dobbs and her inquiry forms part of the Dame Janet Smith Review into the BBC's culture and practices during the years that Jimmy Savile worked at the corporation.
Its conclusions will be published later this year.
Nazir Afzal, chief crown prosecutor North West Area, said: "The convictions for these offences and the offences for which Stuart Hall was imprisoned last year were only made possible by the courage of his victims. I would like to thank them for coming forward and ensuring that he was brought to justice.
"All victims of sexual abuse should know that prosecutors and police will treat these offences with the seriousness they deserve and bring these cases to court where it is right to do so."