Lawyers and campaigners have expressed concern about a large backlog of unresolved Windrush cases, revealed in fresh Home Office figures, two years after Amber Rudd resigned as home secretary amid the emerging scandal.

More than 12,000 people who were wrongly classified by the Home Office as illegal immigrants have now been given citizenship or some other form of documentation proving that they have – and always had – the right to live in the UK. But there are 3,720 outstanding cases with the Windrush taskforce, the body set up to consider applications from people who believe they were wrongly categorised as immigration offenders.

Those decisions triggered often catastrophic problems for the individuals’ access to employment, healthcare, housing and pensions. In extreme cases some of those affected were detained and deported.

Facebook Twitter Pinterest The home secretary, Priti Patel, answers questions from the home affairs select committee on Wednesday, the same day new data on Windrush cases was released. Photograph: House of Commons/PA

The home secretary, Priti Patel, revealed that 1,111 of these cases have yet to be considered, while the others are still under review. More than 150 people have been waiting for longer than six months, and 35 people have spent over a year waiting for a response.

Jacqueline McKenzie, a lawyer who has represented dozens of Windrush cases pro bono, said the backlog might be partly explained by the complexity of the cases, and the fact that individuals were often having to apply for help in untangling their problems, without the support of lawyers or immigration experts.

“The data is indicative of the difficulties people are having in applying to the scheme without professional help,” she said. “There are still people who either don’t know about the scheme or don’t realise that it applies to them and, quite importantly, there are still people who fear that they could be subject to enforcement if they come forward. The stories of people detained and removed from the UK still sends both shockwaves and fear throughout the community of those affected.”

The large number refused under the scheme who applied from abroad triggered concern. Overall, 13,745 people have been refused requests for citizenship or documentation proving their right to live in the UK, of whom 11,332 had applied from overseas. The Home Office said the free application process had attracted a number of “without merit or ineligible claims”.

Facebook Twitter Pinterest People seek information on delays to compensation payments to Windrush victims at a Home Office briefing in Manchester in January. Photograph: Christopher Thomond/The Guardian

Gertrude Chinegwundoh has been trying to assist six friends and family members from Nigeria who spent their childhood in the UK, after being brought here legally by their parents before 1973 but who were later refused reentry into the UK after a trip to Nigeria.

She said all the cases had been rejected under the scheme. “The refusals seem based on flimsy reasons, but these are cases with real merit. One of them has been separated from five siblings in the UK for decades,” she said.

She was disappointed that the government has refused to extend its investigations into the number of people it mistakenly deported.

The Home Office has revealed that it wrongly detained or deported 164 people who were living entirely legally in the UK after emigrating from Caribbean countries. However, officials have refused to attempt to find people who were deported in error to non-Caribbean Commonwealth countries.

“It is not a level playing field; there is no consistency in decision making. The government is still not trying to trace non-Caribbeans who may have been wrongly deported,” Chinegwundoh said.

Windrush report: call for inquiry into extent of racism in Home Office Read more

The Home Office figures reveal that 24 people who were either wrongly detained or deported died before the UK government was able to contact them and apologise for the mistake. Officials are still searching for 14 people who were mistakenly deported to the Caribbean, to tell them they can return to the UK.

The figures showed that only 35 people had been granted “urgent and exceptional support” payments, totalling £46,795, in the two years since it emerged that thousands of people had been wrongly targeted by the Home Office, large numbers of whom were pushed into destitution after being sacked from their jobs or evicted from their homes.

Figures released in February show that compensation payments under a separate scheme have been made to just 36 people, who have shared the total sum of £62,198 paid out from a scheme which was expected to pay out between £200m and £500m.

A Home Office spokesperson said: “We have been clear since the very beginning that no information provided as part of a Windrush scheme application will be used for immigration enforcement action.”

• This article was amended on 30 April 2020 to clarify the period of the first arrival into the UK of the people being helped by Gertrude Chinegwundoh.