One of the London suicide bombers was strolling the corridors of the House of Commons a year before he blew himself up, it was revealed last night.

Mohammad Sidique Khan, who killed himself and six commuters on a Tube train near Edgware Road, attended Parliament as the guest of Labour MP Jon Trickett, in July last year.

The 30-year-old was invited in his capacity as a learning mentor at Hillside Primary School, in Beeston, Leeds, where Mr Trickett's wife, Sarah, is headteacher.

On his visit he also met International Development Secretary Hilary Benn, who talked about his role as the school's MP and answered questions from the children who were with Khan.

The bomber then had a tour of the Palace of Westminster with Mr Trickett, who lived in Beeston, Leeds until he became an MP in 1996.

He said: "It is profoundly disturbing to discover that a person, who appeared to care so deeply for the children at that time, should so callously take the lives of others only a year later."

As the hunt for the bombers' support network continued, Scotland Yard detectives were flying to Cairo after an Egyptian biochemist was arrested there.

Magdy el-Nashar, 33, was detained in Cairo after a search involving Scotland Yard, Interpol, the FBI and other agencies.

Anti-terrorist officers want to speak to Mr el-Nashar about his links to a flat in Leeds and suggestions he knew one of the bombers, Jamaican-born Islamic convert Lindsay Jamal.

Mr el-Nashar studied for his doctorate at Leeds University from October 2000 to May this year.

His degree was sponsored by the National Research Centre, in Cairo, and his work was backed by the regional development agency Yorkshire Forward, which gave him access to £30,000, although that was not taken up.

Police are also looking into links between the bombers and Pakistan-based al Qaida cells.

Intelligence officials in Pakistan believe one of the bombers, Shehzad Tanweer, visited a radical religious school run by a banned Sunni Muslim militant group and that he may be connected to a man arrested for a 2002 attack on a church near the US Embassy.

Meanwhile, detectives in Leeds are trying to establish whether a substance found in a raid is acetone peroxide - also known as TATP.

TATP, which has been chosen for other al Qaida operations in the past, has been an explosive of choice among Middle East extremist groups for many years. It was used by British-born shoe-bomber Richard Reid along with a plastic explosive.

The family of one of the bombers, Hasib Mir Hussain, yesterday issued a statement, saying the 18-year-old was "a loving and normal young man who gave us no concern".

They said: "We had no knowledge of his activities and had we done, we would have done everything in our power to stop him."

Muslims unite - Page 3