Undercover British investigators will be allowed to testify wearing wigs and makeup to conceal their identities at the upcoming US trial of an alleged al-Qaida operative, a judge ruled Wednesday.

The six MI5 agents conducted surveillance on Abid Naseer while investigating a failed plot to bomb a shopping mall in Manchester, England, in 2009. Federal prosecutors plan to call them as witnesses next month at the trial, also expected to feature evidence seized during the Navy Seal raid in 2011 that left Osama bin Laden dead.

At a hearing Wednesday in Brooklyn, US district judge Raymond Dearie approved the disguise request after prosecutors told him in court papers that the officers continue to work undercover on sensitive cases and “disclosure of their identities would pose a significant risk to their safety”.

The agents will testify using identification numbers rather than names and wearing wigs and light makeup, “neither of which will impair the defendant’s or the jury’s ability to view the witnesses’ facial expressions and assess their credibility and demeanor”, the papers added.

Naseer, 28, was extradited in 2013 to New York City where he pleaded not guilty to charges he was part of a broader al-Qaida conspiracy that included the Manchester plot and one against New York City. Two other witnesses expected to testify against Naseer – Najibullah Zazi and Zarein Ahmedzay – pleaded guilty in the thwarted plot to detonate homemade explosives in the subways.

Prosecutors claim that email account evidence shows all three men were under the direction of the same al-Qaida handler. They also say documents recovered during the bin Laden raid – now declassified – confirm the terror network’s leadership was behind the conspiracy.

Naseer has decided to serve as his own attorney at the trial. Opening statements are expected in mid-February.