Benjamin Boateng, the son of Britain's first black Cabinet minister was today jailed for nearly four years for sexually assaulting a woman after a night of West End clubbing.

Benjamin Boateng, 27, whose father is Lord Boateng, displayed "arrogance" towards women and a "proprietary right" to sexual gratification as he assaulted the 22-year-old after she had fallen asleep on the sofa at a party on August 19.

He was jailed for three years and 10 months after a judge ruled the assault at a Battersea flat was pre-planned. The court heard he had "taken the opportunity to satisfy his own sexual gratification after identifying a vulnerable female".

The former actor, who has appeared on The Bill and Grange Hill, also has a caution for harassment from March last year - after he sent "unpleasant" text messages to an ex-girlfriend who eventually called the police.

He had previously been accused of raping an 18-year-old girl in Cape Town after a New Year's Eve party in 2006 when his father was Britain's High Commission to South Africa, but was cleared by police after a 'fast-track' investigation.

His father Lord Boateng was at Kingston Crown Court to see him sentenced along with several members of his family, but refused to comment after sentencing.

Sentencing Boateng, Judge Fergus Mitchell said the 27-year-old "may have attitudes and expectations of women that have allowed the offence to happen".

He said: "You do have a degree of arrogance, and I wonder if you do not feel that you have some sort of proprietary right as part of that arrogance to do as you please.

"It is my view that you targeted and prepared yourself in relation to the event that took place.

"You cosied yourself up to the girl who was at one end of a sofa. You put a cover over both of you. I detect preparation as to what you were going to do.

"She was obviously a vulnerable victim. She was asleep. You thought you could go ahead and do this. Perhaps you didn't think of the consequences but what spurred you on to do it was the attitude you had towards that woman at any rate and I don't know about others.

"She described considerable feelings of humiliation. She has lost a lot of confidence because of what happened."

Boateng, who is now an art curator and entertainment agent arranging London gigs for US celebrities, had been visiting designer friends at London Fashion Week on the 18 August, before heading to the Jet Black Club off Tottenham Court Road at around 3am where he drank champagne and vodka in the VIP area.

The woman had also been in the VIP area and the pair were invited back with a group of friends to the flat, where they met and chatted for "less than a minute."

During the trial, jurors heard she had fallen asleep on the sofa before waking up to find her knickers down, her dress up and Boateng lying beside her.

Disorientated and believing he was her boyfriend, she began to kiss him back but then started to ask him, "where am I?" and "who are you?" He turned around and said 'you're in Battersea, babe.'

Boateng claimed he wasn't attracted to the woman and had placed the quilt over her before settling down to have a nap himself. He said he was in a state of 'disbelief' when she 'hysterically' accused him of touching her. But his version of events was rejected by a jury.

Icah Peart QC, defending, asked the Judge to consider a suspended sentence because of Boateng's "exceptional character."

He said: "The defendant is just 27 years of age. He attended schools in North London and drama school in the north of England, graduating with a degree in drama at the age of 21.

"He has worked as a professional actor and more recently as an entertainments agent since about 2008.

"He is not the sort of person that your honour is used to seeing before him. He is a man of exceptional character. He is so exceptional that an exceptional course may be taken when it comes to sentencing him today."

The judge was handed letters by Boateng's mother and several friends, who described him as "kind-hearted," "thoughtful" and a "true gentleman."

But Judge Mitchell rejected pleas made on Boateng's behalf to allow him to escape prison.

He said: " At the end of the day it has to be imprisonment and I think the public would demand that because of the circumstances of this case and the principle that no woman should be treated in this way, as you treated this woman on that night.

"I don't know whether you appreciate that. I don't know whether you've reflected on the event."

A pre-sentence report concluded that Boateng had "taken the opportunity to satisfy his own sexual gratification after identifying a vulnerable female".

Boateng will remain on the sex offenders register indefinitely.