Mona Thwany became a fanatical Muslim around the time of the Sept 11 attacks and in turn radicalised her previously westernised husband, it is alleged.

Her grandmother Maria Nedelcovici, who lives in Romania, said that Taimur Abdulwahab al-Abdaly could have been persuaded to abandon his deadly bomb plot if his wife had intervened.

She told the Daily Mail: “Mona turned her husband into an extremist. She is the only one to blame. Mona had the power to stop him but she refused. She should have known better.”

Detectives are trying to establish whether Abdulwahab had helpers in Britain after finding a clue on his suicide tape pointing to an accomplice.

A cough that can be heard in the background as Abdulwahab recorded his promise to kill “your children, daughters, brothers and sisters” is thought to be from another person who was with the bomber.

Tomas Lindstrand, Sweden’s chief prosecutor, said: “The attack appears to have been well-planned, and we assume that the suicide bomber had accomplices. We are looking in Sweden, we are looking in England and perhaps even in the Middle East.”

The one-minute suicide tape, which was sent to Sweden’s security police and a news agency by email, detailed Abdulwahab’s intention to carry out mass murder, partly in revenge for Sweden’s military role in Afghanistan.

Antiterrorism officers continued searching Abdulwahab’s home in Luton, where the Iraqi-born bomber, who grew up in Sweden, lived with Mona, his Romanian-born wife. Security sources said no evidence had yet been found of any UK-based attack planning.

British investigators are understood to be focusing on possible links to al-Qaeda in Iraq and the associated group the Islamic State of Iraq, or al-Muhajiroun the banned group with a strong presence at the fundamentalist mosque Abdulwahab attended in Luton.

Mr Lindstrand said: “He was totally unknown to the Swedish Security Police. He came to Sweden from Luton in November so of course it’s important to us to know if there is anything of interest there.”

Explosives experts believe Abdulwahab could have killed 100 people and injured 500, but his car, which was filled with gas canisters, caught fire prematurely and his suicide belt is also thought to have gone off before he intended.

Meanwhile Abdulwahab’s one-time best friend recalled how the bomber had spent time as a community radio station disc jockey in his home town of Tranas, but became withdrawn after he moved to Luton to study physical therapy at Bedfordshire University.

Pelle Johansson said: “He wanted to be a physiotherapist. His ambition was to come back to Sweden and open his own clinic, but something changed when he was in England.” He added: “Taimur liked to play hip hop and pop music and he was popular with everyone, including girls.”