More than 6,000 people in 24 hours have signed up to a campaign to discover if Britain’s communications intelligence agency, GCHQ, has illegally spied on them.

Privacy International launched the campaign in the wake of a court ruling this month that said regulations governing the sharing between Britain and the US of electronic communications intercepted in bulk breached human rights law for seven years until last December.

Privacy International says the decision by the investigatory powers tribunal allows anyone in the world to ask GCHQ if the US unlawfully shared their individual records with Britain. “Did GCHQ illegally spy on you?Have you ever made a phone call, sent an email, or, you know, used the internet? Of course you have,” says the campaign.

Eric King, deputy director of Privacy International, said: “We have known for some time that the NSA and GCHQ have been engaged in mass surveillance, but never before could anyone explicitly find out if their phone calls, emails or location histories were unlawfully shared between the US and the UK. The public have a right to know if they were illegally spied on, and GCHQ must come clean on whose records they hold that they should never have had in the first place.”

King said there were few chances to directly challenge “the seemingly unrestrained surveillance state, but individuals now have an historic opportunity to finally hold GCHQ accountable for [its] unlawful actions.”

Privacy campaigners say they will collate inquiries from people who want to discover if GCHQ spied on them and will submit them to the tribunal. They argue that those who have been found to have been illegally spied on can seek the deletion of their records, including emails, phone calls and internet communications.

Privacy International believes that an unlimited number of people could have been affected by the unlawful spying given the mass surveillance capabilities of the NSA and GCHQ and their “share by default” policy covering the information they collect.

The critical court judgment on 6 February marked the first time since the investigatory powers tribunal was set up in 2000 that it has upheld a complaint against any of the UK’s intelligence agencies. The tribunal said the regulations covering the NSA’s Prism and Upstream programmes were unlawful because the safeguards that were in place had not been made public. Details of those safeguards were only revealed during the course of the legal challenge at the tribunal.

An order posted on the IPT’s website said: “The regime governing the soliciting, receiving, storing and transmitting by UK authorities of private communications of individuals located in the UK, which have been obtained by US authorities … contravened Articles 8 or 10” of the European convention on human rights.

Article 8 relates to the right to private and family life; article 10 refers to freedom of expression.

The intelligence-sharing operations between the NSA and GCHQ only became public following the disclosure of documents by the whistleblower Edward Snowden.

On the day of the ruling, GCHQ disputed the significance of the decision, saying the tribunal had once again ruled that the UK’s bulk interception regime was fully lawful and had rejected accusations of mass surveillance.

The intelligence agency makes a distinction between intrusive mass surveillance, which it insists it does not undertake, and bulk interception of electronic communciations, which it says is necessary to carry out targeted searches of data in pursuit of terrorist or criminal activity.

The GCHQ statement continued: “[The] IPT ruling reaffirms that the processes and safeguards within the intelligence-sharing regime were fully adequate at all times – it is simply about the amount of detail about those processes and safeguards that needed to be in the public domain. We welcome the important role the IPT has played in ensuring that the public regime is sufficiently detailed.”