Iftikhar and Farzana Ahmed denying murdering their daughter Shafilea in a 2004 interview. Both have now been found guilty of murdering her ITN

The parents of Shafilea Ahmed have both been sentenced to life imprisonment with a minimum term of 25 years after being found guilty of murdering their 17-year-old daughter.

The prosecution said Iftikhar Ahmed, a 52-year-old taxi driver, and his wife, Farzana Ahmed, 49, from Warrington, Cheshire, killed the teenager at the family home on 11 September 2003 because they believed she had brought shame on the family with her desire to lead a "westernised" lifestyle.

Shafilea had defied her parents' wishes for an arranged marriage in Pakistan to a much older man. Her body was found on a Cumbrian riverbank in February 2004.

The jury delivered its verdict at Chester crown court on Friday after a three-month trial.

Sentencing Shafilea's parents, the judge, Mr Justice Roderick Evans, said: "What was it that brought you two – her parents, the people who have given her life – to the point of killing her?"

He said: "Your problem was that, in what you referred to as your 'community', Shafilea's conduct was bringing shame upon you, and your concern about being shamed in your community was greater than your love for your child."

The couple had vehemently denied any involvement in their daughter's death.

As the verdicts were delivered after two days of deliberations, Shafilea's brother Junyad and sister Mevish cried in court, as did a younger sibling who cannot be identified for legal reasons. Initially the Ahmed parents remained impassive in the dock, but Farzana Ahmed began crying as she was led out of court, and her husband turned and swore at police officers sitting nearby.

The prosecution's barrister, Henry Riding, said that the two parents acting together had killed their child. "They were her parents and responsible for her care and wellbeing," he said. "In September 2003, she was in a weakened state [after drinking bleach]."

Shafilea's best friend, Melissa Powner, said: "We have waited for this day for many years. We have watched as her killers roamed free. Yet today we heard those important words – words that have finally brought our friend the justice she deserves.

"Shafilea was a caring, high-spirited and brave young lady who even in her toughest times always strived to remain positive and hopeful that one day she too would be able to live the peaceful and happy life that she deserved."

Shafilea's badly decomposed remains were found on a flooded bank of the river Kent in Sedgwick, Cumbria. The jury agreed with the prosecution's assertion that she had been killed by her parents because they believed she had brought shame on the family. In the six months before her death, Shafilea drank bleach during a family trip to Pakistan in an apparent cry for help.

The prosecution's key witness was Shafilea's 24-year-old sister, Alesha, who said she and her siblings had witnessed the murder at the family home. She said Farzana issued the command in Urdu: "Just finish it here," as her parents forced a plastic carrier bag into Shafilea's mouth and placed their hands over her it, blocking her airways as her father held her down. Alesha said Shafilea's eyes were wide open in horror and she was kicking her legs in protest. She realised her sister was dead when her legs stopped kicking.

"That was it, she was gone," she told the court. She recalled seeing her father punching her sister's lifeless body in the chest after the killing. Later, she watched her mother prepare sheets, binbags and rolls of tape in the kitchen. She looked out of a window and saw her father carrying a heavy package, which she assumed was Shafilea's body.

Iftikhar Ahmed denied any part in his daughter's death and maintained that Shafilea ran away from home in the middle of the night and he never saw her again. His wife changed her account of events midway through the trial and said her husband was responsible for a single, violent attack on Shafilea on the night of her disappearance. Her husband, she claimed, told her to never ask him about Shafilea again "if she cared for her dear life" and those of her children. However, the jury failed to be convinced by either of the couple's versions of events and found them both guilty.

The judge said Iftikhar Ahmed came to the UK when he was 10 and was fully familiar with western culture. He married a Danish woman, had a son with her, and lived for a time in Denmark. He returned to Pakistan in 1985 to marry Farzana, his cousin, who had "no experience of western culture". The couple returned to the UK in 1986 when Farzana was pregnant with Shafilea.

"You chose to bring up your family in Warrington, but although you lived in Warrington, your social and cultural attitudes were those of rural Pakistan and it was those you imposed on your children," the judge said.

The judge said Shafilea was a "determined, able and ambitious girl who wanted to live a life which was normal". But the couple wanted their family to "live in Pakistan in Warrington". He said the couple objected to their daughter socialising with girls from the white community, wearing western clothes and having contact with boys.

"She was being squeezed between two cultures: the culture and the way of life she saw around her and wanted to embrace, and that they wanted to impose upon her," Evans said. He said the conflict increased in the final year of her life when her parents tried to impose their cultural values and attitudes by "intimidation, bullying and the use of physical violence". When she was taken to Pakistan it was to be "sorted out", the judge added, to have her westernised ideas removed and to be married off.

When Shafilea ran away in February 2003, she was recaptured and dragged off the street and forced into a car. "A week later she was drugged and taken to Pakistan," the judge said. "I have no doubt that your intention was she should remain in Pakistan and be married there."

After drinking bleach Shafilea's condition deteriorated to such an extent that "she was no longer wanted as a bride".

The judge said the couple may have discussed the way they might resolve the problem Shafilea presented them before the day of the killing.

The judge added: "You killed one daughter, but you have blighted the lives of your remaining children. Alesha escaped but she is unlikely to avoid the legacy of her upbringing. Mevish, after a period of trying to live independently, was recaptured and brought home and has since become compliant. She came to court and was placed in the sad position of having to deny her own words in order to try and help the parents she and no doubt all your surviving children still care for."

He said there was only one sentence he could impose and that was life. He set a minimum term of 25 years before either parent was eligible for parole. The aggravating factors included that they acted as a team, they were the people to whom Shafilea should have been able to look for protection and kindness, she was vulnerable when they killed her "and a truly horrifying feature", he said, "is that you killed Shafilea in the presence of your other four children".

He added that after the killing they concealed the body and not only did they lie to mislead people, including the coroner, but "you also made your surviving children put forward an account which was intended to hide what you did".