The watchdog charged with holding MI5 to account rewrote a report into the handling of a violent neo-Nazi agent after the Security Service gave it false information, the BBC can reveal.
An early draft of the report by the Investigatory Powers Commissioner's Office (IPCO) contradicted false evidence given by MI5 to court, but the final version did not.
IPCO told the BBC it was "misled" by the Security Service.
MI5 director general Sir Ken McCallum apologised to IPCO, after the BBC challenged the Security Service's false statements to the courts.
The revelation means that MI5 has effectively given false evidence in this case to every organisation or court which is supposed to have access to the Security Service's secrets and is responsible for holding it to account.
