Police believe a gifted student convicted today of attempting to stab to death a former government minister for supporting the Iraq war is the first Briton to have been inspired by al-Qaida to assassinate a politician on British soil.

Police and those close to Roshonara Choudhry have both told the Guardian she was radicalised after watching sermons she downloaded off the internet given by Anwar al-Awlaki.

Awlaki is an Islamist cleric, now in Yemen, who the United States suspects was the mastermind of several terrorist plots. Top of those is the attempt uncovered on Friday to send bombs on cargo travelling in planes, which sparked a worldwide terrorist alert.

At the Old Bailey in London today Choudhry, 21, was convicted on three charges after a short trial in which she ordered her defence team not to challenge the prosecution's case. The jury took just 20 minutes to return unanimous verdicts on the attempted murder charge and two counts of having an offensive weapon.

On 14 May 2010 she stabbed her local MP Stephen Timms twice in the stomach. She confessed to the attack to police later that day.

The case, thought to have resulted initially from mental illness, was taken over by Scotland Yard's counter terrorism command, after the link to al-Awlaki was discovered on Choudhry's computer and after she told detectives in interviews after her arrest she had watched the extremist's sermons. Al-Awlaki is the "spiritual leader" of al-Qaida in the Arabian Peninsula.

The court heard Choudhry wanted to stab Timms to death as "punishment" for voting for the Iraq war. Timms, who was a minister in both the Blair and Brown governments, was attacked at his constituency surgery in east London. The attack came days after Labour lost power.

Choudhry raises her right hand in the attack. Photograph: Metropolitan police

Her conviction highlights the concern police and the authorities have about "self radicalisation", where people turn to Islamist violence after finding material themselves on the internet urging a holy war against the west, and become convinced by it.

A senior source told the Guardian that Choudhry turned to violence after being inspired by al-Awlaki's sermons urging that the alleged western oppression of Muslims demanded a violent response.

The senior source said: "She was inspired by his sermons, and radicalised by watching them.

"His message is do anything, whatever you can."

It is the first terrorist attack to injure someone on the UK mainland since 7 July 2005.

Choudhry, 21, "smiled" just before plunging the knife into the abdomen of Timms, who was saved when an aide grabbed the knife and a security guard put Choudhry in a "bear hug".

She told police during interview under criminal caution that she was intent on stabbing the MP to death, the court heard. Weeks before, she had bought two new knives for the attack, one with a three-inch blade which she used in the stabbing; the other, with a five-inch blade, was kept in her handbag as back up in case the first broke during the attack, she told officers.

After her arrest, Choudhry explained she stabbed Timms in the stomach because it was a soft area of the body and she feared being too weak to force the knife into another area.

The Old Bailey jury was told she was not mentally ill and was calm after the attack. The incident was captured on CCTV, stills of which were shown to the jury.

Choudhry, the jury was told, does not recognise the jurisdiction of the court.

The jury heard that she had told detectives: "I was not going to stop until somebody made me." Interviewed hours after the attack, Choudhry told officers: "I was trying to kill him."

When the interviewing officer, Detective Inspector Simon Dobinson, asked why, she replied: "Because he wanted to invade Iraq." Asked what that would achieve, she said: "Punishment." She later added: "I was hoping to get revenge for the people of Iraq."

Choudhry, who was not in court, was convicted of attempted murder and two charges of having an offensive weapon.

She will be sentenced on Wednesday, and her family are said to be devastated by the fate of their eldest child, who wanted to become a teacher.

Choudhry had been a student in English and communications at King's College, London, and in her first two years had been a prize-winning student who was predicted to get a first. She was also a gifted linguist who was fluent in Arabic, Bengali, and French.

She dropped out of her studies at the start of 2010 and began downloading extremist material, according to police examination of her computer, around the autumn of 2009.

Choudhry appears to have no links to known extremist groups.

On the day of the attack, Choudhry took a bus from her East Ham home to Timms's constituents' surgery at the Globe community centre in Beckton, east London. Choudhry asked to see Timms, who is her local MP, rather than his assistant. She then waited for her appointment.

She approached the desk where Timms was sitting. He told the court he got up, and thought her left hand was outstretched because she wanted to shake hands. He added that Choudhry appeared to be "smiling" and "friendly".

Timms told the jury: "I was a little puzzled because a Muslim woman dressed in that way wouldn't normally be willing to shake a man's hand, still less to take the initiative to do so, but that is what she was doing. She lunged at me with her right hand."

The court heard while her left hand was outstretched, Choudhry used her right hand to stab the former minister. Dobinson said Choudhry told him during the police interview: "I purposefully walked round the side of the desk so I could get close to him. He pointed for me to sit down on the chair but instead I walked towards him with my left hand out as if I wanted to shake his hand."

She thought he had shaken her left hand with his left hand, but she could not remember. Her right hand had been in her pocket.

She continued: "Then I pulled the knife out of my bag and I hit him in the stomach with it. I put it in the top part of his stomach like when you punch someone."

She managed to stab Timms a second time before she was pulled off.

Nigel Tai, the surgeon who operated on Timms, described the injuries he suffered as "potentially life threatening" because of the possible loss of blood and infection had he not been treated.