Suspect profileBritish anti-terrorist officers were due in Cairo today to interview an Egyptian, Magdi al-Nashar (33) of Leeds University's school of biochemistry and microbiology, as his home in Leeds was searched.
Mr al-Nashar, who is reported to have recently applied for an academic post in Ireland, has denied any connection with the bombings.
He said he has been on holiday in Egypt, and fully intends to return to England.
Mr al-Nashar recently completed five years of studies and returned to Egypt about four weeks ago.
A friend, Will Voller, a 23-year-old nurse who prayed at the same mosque as the biochemist, said: "He is a good, friendly, hospitable man. I can't believe that he is mixed up in this.
"He was very active at the mosque, helping with things like open days for local schoolchildren."
Mr al-Nashar was awarded his PhD in May after being sponsored by an organisation in Cairo called the National Research Centre (NRC) to study biochemical techniques for use in food and environmental science.
Before arriving in Leeds he studied in North Carolina, and the FBI is looking into his record while there .
Mr al-Nashar knew some of the suicide bombers, security sources said, though police have not yet formally named him as a suspect.
He emerged on a police suspect list after he was linked to one of the houses in the Leeds area used by three of the suicide bombers before they travelled to London.
Colleagues in Leeds said they had not seen him since early July.
The head of the Egyptian NRC which sponsored Mr al-Nashar's research said he delivered his PhD thesis to the chemistry department the week before the London attacks, and that he had spent time with colleagues there.
Leeds University said Mr al-Nashar came to Leeds to study for a PhD in the school of biochemistry in October 2000.
His subject was "Development of a novel matrix for the immobilisation of enzymes for biotechnology" .
He was working on a project backed by a regional development agency, Yorkshire Forward, which gave him access to €30,000 but that was not taken up.
A man who knew the scientist told the Yorkshire Post: "He was extremely charming and very intelligent, a very typical Egyptian with perfect manners.
"He was obviously quite a brilliant chemist."
The man said there was "nothing remotely sinister" about his work.
"It's like making margarine. It's straightforward and highly commercial," he told the paper.