Only half of the Home Office’s recent asylum decisions have met its own internal quality checks, significantly fewer than before Rishi Sunak’s push to clear a backlog of old claims.

Civil servants and lawyers say errors and omissions are also driving a huge increase in costly legal challenges, with more than 9,300 appeals lodged between this April and June.

Only 52% of asylum decisions sampled in the Home Office’s internal quality assurance process were satisfactory in 2023/24, new figures show, down from 72% the previous year.

In the same period, the number of appeals against asylum decisions lodged at the First-Tier Tribunal rose from 8,000 to 29,000. Almost half of challenges are currently successful.

An asylum official who spoke to the Observer on condition of anonymity said changes implemented after former prime minister Sunak’s pledge to process more than 90,000 old asylum claims by the end of 2023 had made decisions less safe.

“They significantly shortened the training period for asylum decision-makers,” they added. “They raised the targets to clear the backlog, focusing on quantity rather than quality. Decision-makers were expected to crank out seven ‘events’ a week, come hell or high water, and that adversely impacted on the quality of their decisions.”

The Home Office also introduced a two-hour limit for most asylum interviews, which the official said “made it very difficult to gather enough information to write a sustainable decision that could withstand legal scrutiny”, and “concise” templates for explaining refusals.

The quality assurance process was also downgraded during the push to clear the legacy backlog, with an internal Home Office report from June 2023 warning of “insufficient activity to identify risks” and a “risk of incorrect or unsustainable decisions”.

The asylum processing changes have been maintained since the general election, the Observer understands, despite Sunak declaring the legacy backlog “cleared” in January.

The Freedom from Torture charity called the quality assurance figures “alarming”. Head of asylum advocacy Sile Reynolds said: “If quality is sacrificed in the pursuit of efficiency, then we risk sending refugees back to torture and persecution.

“If this government doesn’t want to repeat the mistakes of the previous government, then it needs to urgently prioritise quality alongside speed.”

Lily Parrott, a solicitor at Duncan Lewis who specialises in asylum claims, said she and her colleagues had “noticed a drop in decision-­making quality”.

She added: “We’ve been seeing a lot more unexpected refusals, and we’re very conscious that will probably just move the backlog from the Home Office to the tribunal. As the quality of decisions goes down, that’s leading to more refusals and more appeals.”

Parrott said errors in asylum refusals included decision letters with the wrong name, the wrong nationality, the wrong gender, and where “they’ve been clearly copying and pasting sections of other people’s decisions”.

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The Observer has also been told of cases where the Home Office booked interpreters for asylum interviews who spoke the wrong dialect, generating inaccurate records of applicants’ testimony as a result.

The Immigration Law Practitioners’ Association said members were seeing “factual mistakes”, failures to consider evidence and “poor-­quality interviews”. It added: “The Home Office is refusing cases on the basis that it does not believe individuals are at risk, because there is insufficient detail about the risk of persecution, while simultaneously appearing not to seek that detail or information.”

The Care4Calais charity said mistakes had a “profound” impact on vulnerable asylum seekers, who face “further needless anxiety, uncertainty and months in limbo for appeals to be processed”.

Hannah Marwood, the charity’s head of legal access, said: “These poor-quality decisions will wreck people’s lives by denying them the right to safety and protection.”

A Home Office spokesperson said: “The government is determined to restore order to the asylum system so that it operates swiftly, firmly and fairly. We are getting the asylum system moving again by processing cases and increasing returns of people who have no right to be here.”