London bombers were local, independent

The suicide cell that killed 52 people on 7 July is not linked to those alleged to be behind the second London attacks on 21 July, according to the initial findings of the biggest anti-terrorist investigation held in Britain.

An investigation into the four suicide bombers from the first attacks and the people alleged to be behind the July 21 plot has found no evidence of any al-Qa'ida "mastermind" or senior organiser. The inquiry involved MI5, MI6, the listening centre at GCHQ, and the police.

The disclosure that the July 7 team were working in isolation - and were radicalised by Mohammad Sidique Khan, the oldest man - has caused concern among anti-terrorist officers.

Police and MI5 fear it increases the chance that more "self-sufficient" units similar to the July 7 suicide cell are hiding in Britain. Anti-terrorist officers are worried by the evidence that previously unknown "clean skin" terror cells are forming in Britain with little or no help from abroad.