An expanded watchdog charged with regulating the intelligence services and surveillance by state agencies has officially begun work.

The role of the first investigatory powers commissioner, Lord Justice Fulford, combines the work of three former oversight bodies and will provide judicial checks on some investigations. His office, the IPCO, will employ about 70 staff, including 15 serving and retired judges.

Inspectors will check that the interception of phone calls, and the handling of agents, surveillance and powers permitting bulk collection of communications data are carried out within the law.

Among organisations overseen by the IPCO are the government’s monitoring agency GCHQ, MI5, MI6, the National Crime Agency, all police forces, the Serious Fraud Office, HM Revenue and Customs, local authorities, prisons and government departments.

The body replaces the work of the previously separate surveillance commissioner, interception of communications commissioner and intelligence services commissioner.

Sir John Goldring, the outgoing intelligence services commissioner and a retired former court of appeal judge, will be Fulford’s deputy.

Fulford is the senior presiding judge for England and Wales and has served as a judge at the international criminal court in The Hague.

He said: “From today, and for the first time, investigatory powers will be overseen by a single body applying a consistent, rigorous and independent inspection regime across public authorities. This is an important milestone as we start to implement the new oversight powers set out in the Investigatory Powers Act.”

Among the most sensitive work of the agency will be operation of the “double-lock” system of authorisation of interception warrants introduced by the act. Under the scheme both a minister and an independent judge, known as a judicial commissioner, will have to approve surveillance warrants.

Human rights groups and MPs have questioned whether the judicial commissioners will be given sufficient access to secret information to make their role more than that of a rubber stamp.

The IPCO team, which starts work on Friday, includes inspectors, technical and legal advisers, and scientists on a technology advisory panel.

The previous commissioners’ posts have been abolished, but their final annual reports will be published soon.

Operation of the new act remains highly controversial. The human rights group Liberty has launched a crowdfunded legal challenge to the “sweeping state spying powers” it contains.