Newsnight editor Ian Katz has spoken of his concern over the seizure of a BBC journalist's laptop by police acting under the Terrorism Act.
Secunder Kermani handed over the computer after officers secured a judge's order, the BBC has confirmed.
They were responding to communications between Kermani and a man in Syria who was publicly identified as an Islamic State extremist.
Police said the laptop, seized after a hearing in August, had been returned.
Police have legal powers to seize information during any inquiries into the "commission, preparation or instigation of acts of terrorism", under the Terrorism Act which was introduced in 2000.
Katz said police use of the act to access information shared between journalists and sources could cause problems when reporting about the Islamic State (IS) group.
"While we would not seek to obstruct any police investigation, we are concerned that the use of the Terrorism Act to obtain communication between journalists and sources will make it very difficult for reporters to cover this issue of critical public interest," Katz said.
Thames Valley Police said it would be "inappropriate" to talk about any "ongoing live investigation".
But it said: "The BBC attended the hearing in August and did not contest the application or decision of the court. Police have since returned the laptop that was the subject of this order."
It is understood that there were lengthy negotiations between the BBC and the police force before the court order was made.
Kermani, who has previously worked for BBC London, Channel 4 News and the Islam Channel, joined Newsnight last year.
During his work for the current affairs program he interviewed a number of people claiming to be connected to IS, including Jake Bilardi, an 18-year-old Australian whose photo with IS fighters appeared online last December.
A BBC spokesman said: "The BBC does everything it can to protect its reporters' communication and materials and sought independent expert legal advice in the case of Secunder Kermani.
"It did not resist Thames Valley's application for an order under the Terrorism Act in court because the act does not afford grounds under which it could be opposed.
"It is troubling that this legislation does not provide the opportunity for the media to mount a freedom of speech defence."