Britain's anti-terror law watchdog has said police should no longer be able to detain people at the UK's borders without any suspicion of wrongdoing, following the detention of David Miranda in August.

Theresa May, the home secretary, will come under pressure to change the law after David Anderson QC, the independent reviewer of terrorism legislation, gave new advice on the controversial schedule 7 of the Terrorism Act relating to detention at ports and airports.

In a note to the House of Commons home affairs committee, Anderson said that he was setting out new advice after the legislation was put under the spotlight in a number of incidents this summer.

One was the nine-hour detention of Miranda, whose journalist partner, Glenn Greenwald, was involved in exposing the extent of US and UK spying based on leaks by the whistleblower Edward Snowden. At the time Greenwald worked for the Guardian.

Anderson said there must be grounds for suspicion that someone is involved in terrorism before they are held at the border.

He said this test should also apply before any data is downloaded and copied by the authorities. At present, a person can be detained for up to nine hours, without any grounds for suspicion, to determine whether they may be "concerned in the commission, preparation or instigation of acts of terrorism".

Anderson's new guidance comes as the Guardian's editor-in-chief, Alan Rusbridger, is due to appear before the home affairs committee on Tuesday to answer questions about the paper's reporting of surveillance by GCHQ and the US National Security Agency.

Miranda has sought a judicial review of his detention, arguing it was a misuse of the act and breached his human rights.

The legislation was also opened up to challenge under the European convention on human rights in May, was called into question by the supreme court in October and criticised by parliament's joint committee on human rights in the same month. The row over schedule 7's powers broke out after Miranda was detained in London while returning to his home in Rio de Janeiro from Berlin. It was alleged that officials confiscated electronic equipment, including his mobile phone, laptop, camera, memory sticks, DVDs and games consoles.

During his trip to Berlin, Miranda visited Laura Poitras, the US film-maker who has been working with Greenwald and the Guardian. The Guardian had paid for Miranda's flights as he often assists Greenwald in his work, although he was not a Guardian employee.

Anderson has previously said parliament should consider the "necessity and proportionality" of schedule 7 powers, but he set out more detailed views at the request of Damian Green, the policing minister, and senior Liberal Democrats.

Under his proposals, officials would still be able to search and question passengers without grounds for suspicion but any delay of more than an hour would need to pass the extra threshold test for a detention. About 60,000 people were questioned last year under schedule 7 powers, while 670 were formally detained, which Anderson said had given rise to resentment among some Muslim groups who feel they are being singled out.

"My recommendations for further reform include the introduction of a suspicion threshold for the exercise of some schedule 7 powers, and the improvement of safeguards in relation to private electronic data and other sensitive material of various kinds," Anderson said. "I do not believe that anything in my recommendations should reduce the efficacy of what is a very useful set of powers, or expose the public to additional risk from terrorism."

The watchdog also said there should be a ban on using any admissions by someone being questioned during a schedule 7 interview in a subsequent criminal trial and recommended tougher safeguards on how data is retained and stored. However, he stopped short of advising "reasonable grounds for suspicion" before detention, as some campaigners have sought.

The government is now facing calls to amend the antisocial behaviour, crime and policy bill to include Anderson's recommendations. The bill already contains a clause reducing the maximum detention time from nine to six hours, after the watchdog said it should be scaled back.

Julian Huppert, a member of the home affairs committee, said the law should be changed and there was a case for the powers to be revised even further.

"I'm very pleased to see David Anderson's proposals for further constraints on schedule 7. His suggestion to require grounds for suspicion for detention and constraints on the use of private electronic data are very welcome. They should be implemented as a bare minimum."

Following the Miranda detention, Yvette Cooper, the shadow home secretary, called for an urgent investigation into the use of schedule 7, saying Miranda's detention caused "considerable consternation".

"Any suggestion that terror powers are being misused must be investigated and clarified urgently," she said. "The public support for these powers must not be endangered by a perception of misuse.

Previously, Anderson has warned that schedule 7 must be used proportionately and recommended that the maximum detention period be reduced. He is also reviewing the use of the powers in the Miranda case.

In his new recommendations, he said: "I announced in August my intention of publishing a report into the detention of Mr Miranda. It soon became clear that much of the relevant ground would be authoritatively covered in his judicial review proceedings, which have been expeditiously handled on all sides and in which argument was heard on 6 and 7 November. Once judgment is handed down, I propose to decide what more I can usefully add, including by way of any additional recommendations relating to schedule 7."

Schedule 7, which applies only at airports, ports and border areas, controversially allows officers to stop, search, question and detain individuals. Miranda was held for nine hours, the maximum the law allows before officers must release or formally arrest the individual.

Asked whether Anderson's recommendations would be accepted, a Home Office spokesman said: "Schedule 7 forms an essential part of the UK's security arrangements at the border. We are already making changes to these powers to further strengthen the safeguards around their use – these are currently before parliament."