The Information Commissioner’s Office must “urgently investigate” the Conservative party for possible “illegal use of data”, according to Labour’s Stephen Kinnock, after it repeatedly refused to answer a series of questions over its use of personal data.

Under the 1998 Data Protection Act, it can be illegal to process ‘sensitive’ data – a category that includes ‘political opinions’ – without explicit consent from the individuals concerned, although consent is only one of a number of conditions under which sensitive personal data may be legally processed. But despite numerous attempts by the Observer to contact Conservative HQ last week, the party refused to say if it is using any data, modelling or insight gathered during the referendum campaigns for use in the current general election.

Kinnock, the Labour candidate for Aberavon, who has filed complaints with the CPS and Metropolitan Police regarding what he believes are breaches of the law by the Leave campaigns – claims which they deny – said the refusal to give clear answers about the possible use of that data in this election raised urgent new questions.

“The Tories need to urgently disclose exactly what data they have and what they are doing with it. It’s illegal to collect sensitive political data for one purpose and then use it for another. The Data Protection Act clearly states that.

“You can’t have a functioning democracy without transparency. It’s clearly in the public interest to have this information. This must now be referred to the Information Commissioner’s Office, which needs to give this their urgent attention. The election is less than two weeks away, and the authorities have an obligation to defend our democracy.”

Earlier this month, the information commissioner, Elizabeth Denham, announced that the office would be “deepening our current activity to explore practices deployed during the UK’s EU referendum campaign” and had opened “a formal investigation into the use of data analytics for political purposes”.

She also said she would “remind all relevant organisations of the need to comply with the law. I have written to all major political parties with our updated guidance on campaigning.”

Will Straw, the head of the Stronger In campaign, echoed Kinnock’s call, saying: “The Information Commissioner’s Office should launch an urgent investigation.” He said it was a matter of urgency given the election is only two weeks away.

He added: “Since the Conservative party was neutral in the referendum, the public have a right to know if they are now benefiting from data or insights gathered from the Leave campaign.”

Martin Moore, director of the Centre for the Study of Media, Communication and Power at King’s College London, who has studied the rapid and radical changes that digital campaigning has brought to the political landscape in Britain, said there were “urgent questions to be answered about Vote Leave’s data”.

He has been searching for answers about use of data during the referendum, and contributed to an LSE report published in April that called for “an urgent review” of UK electoral law.