Britain's security services consistently prevented Scotland Yard from pursuing investigations against Anjem Choudary, it has been claimed.
Many have wondered why it took so long to arrest the hate preacher; with some suggesting the case has demonstrated failings in the British legal system.
An unnamed source cited in the Telegraph has claimed counter-terror officers believed they had enough evidence to make a case around Choudary and his radicalisation of others.
However it is claimed that MI5 then told them to hold off, as he was part of their own on-going investigation.
Choudary was convicted last month, after swearing an oath of allegiance to Isis and praising the group online. He faces up to 10 years in prison, and will be convicted on September 6.
Police believe the lawyer-turned-preacher was linked to at least 15 terror plots since 2001, and he may have connections to around 500 British Muslims who have now travelled to Syria to join the Islamic State.