The Home Office has admitted that the number of Windrush people known to have been wrongly deported or detained is likely to rise from the figure of 164, because officials have misclassified a number of affected people as criminals and excluded them from the count.

The admission prompted Labour’s Harriet Harman to accuse the Home Office of “blundering in their attempt to sort out a Home Office blunder”.

As part of its response to the Windrush crisis, the government conducted an official review of 11,800 cases of Caribbean-born people who have been detained or removed since 2002 to assess how many might have been mistakenly targeted despite being legally in the UK.

The home secretary, Sajid Javid, took the decision in August to exclude from that review anyone with a criminal conviction, and announced that there were 164 people who were likely to have been wrongly detained or removed from the UK. However there was unease about the decision not to count those classified as “criminal case types” and confusion about what that classification meant.

The Home Office has now conceded that its “criminal case type” category wrongly included people who had no criminal convictions, and has agreed to revise its calculation of the total number of people mistakenly removed or detained.

Responding to a request for greater clarity from the parliamentary joint committee on human rights, Javid said a decision had been taken to revise the methodology, because it had emerged that the category of “criminal case type” was too broad and had included individuals who had “committed only a minor offence/s or have been acquitted or not prosecuted”.

Harman, the chair of the joint committee, said: “The committee’s probing of this issue has revealed that Windrush people who’d been acquitted of criminal charges, or charged but never prosecuted, were nonetheless excluded from the Home Office review because they were subject to ‘criminal case markers’.

Profile How the Guardian broke the Windrush story Show In November last year, Paulette Wilson (left), who has lived in the UK for more than half a century, spoke to the Guardian's Amelia Gentleman about her treatment at the hands of the Home Office - and revealed that she had been held at Yarl’s Wood detention centre and threatened with deportation. It was the first of a series of stories that developed a picture of how many members of the Windrush generation were being mistreated by the government under the so-called ‘hostile environment’ policy. By February, with other examples mounting, the government had relented in Wilson’s case, but faced acute criticism from Caribbean diplomats who urged the Home Office to adopt a “more compassionate” approach. In March the story of Albert Thompson - who had lived in Britain for 44 years but was told to produce a passport or face a bill of £54,000 for cancer treatment - forced attention back to the growing crisis. After the Guardian reported a string of additional cases matters came to a head when Theresa May refused to meet with Caribbean diplomats to discuss the issue, prompted fury among opposition MPs and a wider media backlash. After days of negative publicity, the then home secretary, Amber Rudd, and May were forced to change tack and issued apologies, promised reforms – and eventually gave the Windrush generation a fast-track to citizenship. Photograph: Fabio De Paola

“The Home Office appear to be struggling to grasp even the fundamentals of tackling such a serious injustice.”

The admission follows the revelation earlier this week that eight more members of the Windrush generation believed to have been wrongly detained or deported had subsequently died, bringing the total to at least 11 deaths after removal or detention.

Javid has admitted that British officials are struggling to contact many of those thought to have been wrongly removed, which could mean that the final death toll will be higher.

A Home Office spokesperson said: “As the Home Secretary said in his letter to the Joint Committee on Human Rights, work is underway to review previously excluded cases.

“We will continue to keep both the JCHR and the Home Affairs Select Committee updated on the progress of this work.”

