The BBC did not contest a court order issued under the Terrorism Act to seize the laptop of a Newsnight journalist, police said.
The laptop of Newsnight journalist Secunder Kermani, who has interviewed British-born jihadis and so-called Islamic State (IS) fighters, was seized by police using powers issued by a judge.
In a statement on Wednesday, the BBC confirmed the incident but refused to release details of the police force involved.
Thames Valley Police have now been revealed as the force that seized the laptop, but said the BBC "did not contest" the court's decision.
A spokesman for the force said: "In order to obtain a court order, officers would have to satisfy the Crown Court that there were sufficient grounds to justify the issue of a Production Order under the Terrorism Act. The Respondent in any such process can contest the Order which can then be heard at a higher court.
"In this particular case, 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."
Police have far-reaching powers under Section 32 of the Terrorism Act 2000, which deems any police inquiry into the "commission, preparation or instigation of acts of terrorism" to be termed a "terrorism investigation".
Editor of Newsnight, Ian Katz, said: "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."
A BBC spokeswoman said the man featured in reports "was not a confidential source".
Kermani, who has previously worked for BBC London, Channel 4 News and the Islam Channel, was criticised last year for a Newsnight interview with a British-born IS fighter.
"Awlaki", a 27-year-old British Pakistani fighter, told Kermani he hated the UK and joked about the group beheading its enemies.
Conservative MPs Michael Ellis and Nigel Evans lambasted the BBC programme for running the interview, saying it gave the group a mainstream media platform.
Kermani developed contact with Awlaki over several months and said the jihadi was "softly spoken". The BBC said the report "offered insights" into IS crimes.