The Home Office is yet to make decisions on thousands of asylum applications from before June 2022 despite Rishi Sunak’s promise to clear the legacy backlog.

Caseworkers have been offered financial incentives to help hit the prime minister’s target of processing 92,000 cases from before June 2022. But in a statement released on Monday, the department said 4,500 complex cases from the backlog were still subject to further investigation.

Officials say that 86,800 decisions have been made after the government stepped up processing and deployed an additional 1,200 caseworkers.

In December 2022, Sunak pledged to tackle the remaining legacy asylum backlog by the end of 2023. The backlog had more than 92,000 cases of individuals who claimed asylum before 28 June 2022 which were waiting for an initial decision.

A statement from the Home Office on Monday said: “While all cases have been reviewed and 112,000 decisions made overall, 4,500 complex cases have been highlighted that require additional checks or investigation for a final decision to be made.

“These hard cases typically relate to asylum seekers presenting as children – where age verification is taking place; those with serious medical issues; or those with suspected past convictions, where checks may reveal criminality that would bar asylum.”

The statement came in a press release that said “the prime minister’s commitment of clearing the legacy asylum backlog has been delivered”.

A Conservative source said the Home Office’s claim to have cleared the backlog was clearly wrong. “You’ve either cleared all the cases and made decisions or you haven’t. And they haven’t,” they said.

Enver Solomon, the chief executive of the Refugee Council, said: “It is misleading for the government to claim that the legacy backlog has been cleared as there are thousands still waiting for a decision and almost 100,000 waiting in an additional backlog created by the government’s unfair and draconian new laws, including the unlawful Rwanda plan, that have left men, women and children feeling anxious and fearful resulting in some self-harming and becoming suicidal.

“The Home Office has lost track of too many people who have been removed from the asylum process and at the same time left those who have been granted refugee protection to fend for themselves, at risk of sleeping rough during the winter months.”

Bonuses offered to asylum caseworkers working on the legacy claims increased as the deadline approached. In November, if a caseworker completed three extra shifts in a calendar month, they would get £75 for the first shift, £100 for the second and £125 for the third, which would be paid in vouchers.

In December, the Home Office doubled the overtime rate for two weekends so that a worker could get £150 a shift in vouchers on top of their normal pay.

Insiders say many asylum claims from the legacy backlog have been dismissed in the knowledge that they will be resubmitted but will no longer count as legacy claims. Instead, they will be defined as “secondary asylum casework”.

A Home Office insider said this amounted to “fiddling the figures”. They said: “Many cases are dropped because claimants have not filled in questionnaires on time or have failed to attend an interview. Their forms will be resubmitted and the claims recategorised, but no longer part of the legacy backlog. It looks like a way of fiddling the figures to hit the PM’s target.”

The Home Office has been asked for a breakdown of the number of cases that were legacy cases and are now “secondary asylum casework”.

Clearing the legacy asylum backlog has been seen by the Home Office as a pivotal step in the government’s aim to stop the boats. End-of-year statistics showed small boat crossings were down by 36% in 2023.

Sunak said: “By clearing the legacy asylum backlog, deciding more than 112,000 cases, we are saving the taxpayer millions of pounds in expensive hotel costs, reducing strain on public services and ensuring the most vulnerable receive the right support.

“But we cannot be complacent, which is why I am focused on delivering on my commitment to stop the boats and get flights off the ground to Rwanda.”