The backlog of cases in criminal courts in England and Wales is likely to be a pervasive issue for several years, severely affecting victims, witnesses and defendants, the National Audit Office has said.

In a report published on Friday, the NAO says the Ministry of Justice’s plan to tackle the backlog is ambitious and hinges on securing funding and resources, neither of which are a given.

Parliament’s spending backlog says uncertainty around funding, physical and judicial capacity in courts and the capacity of other criminal justice agencies and support services all pose a threat to the recovery. Additionally, the MoJ and Her Majesty’s Courts and Tribunals Service (HMCTS) are described as “not yet working towards shared, strategic objectives” with respect to the backlog.

The report chimes with grave warnings from lawyers and observers. It says the backlog in the crown courts, which hears the most serious cases, had already increased by 23% in the year leading up to the coronavirus pandemic, partly because the MoJ allocated an insufficient number of court sitting days. Despite a quick response by the MoJ and HMCTS to the pandemic, the NAO says the number of cases received and not yet completed in the crown courts increased by another 48% in the 15 months to the end of June, to 60,692.

In the latter period, the number of cases older than a year in the crown court increased from 2,830 to 11,379 (302%), and from 246 to 1,316 (435%) for rape and sexual assault cases.

Gareth Davies, the head of the NAO, said: “Despite efforts to increase capacity in criminal courts, it looks likely that the backlog will remain a problem for many years. The impact on victims, witnesses and defendants is severe and it is vital that the Ministry of Justice works effectively with its partners in the criminal justice system to minimise the delays to justice.”

The report also expresses concern about how court users who are vulnerable because of their age, mental disorders or physical impairment have been affected, for example by remote access to justice, accusing the MoJ and HMCTS of a “poor understanding” of the issue.

“We also found no evidence that the ministry and HMCTS have any data on users’ ethnicity to carry out meaningful analysis on whether ethnic minority groups have been disadvantaged by the pandemic or the recovery programme. The ministry is therefore unable to assure itself that it is meeting its objective to ‘build back fairer’,” the report says.

The MoJ’s latest models indicate the crown court backlog could be between 17% and 27% higher than pre-pandemic levels by November 2024. But the NAO says both scenarios assume increasing the use of part-time judges to “unprecedented levels”, adding: “Considerable uncertainty remains about demand flowing into the courts following the pandemic and the pace of new police recruitment and deployment.”

An MoJ spokesperson said: “This report recognises the speed at which we responded to Covid-19. This meant that in a matter of months our buildings were made safe, remote technology was rolled out across all courts, and Nightingale courtrooms opened up and down the country to increase the space available for trials.

“We are already seeing the results, with outstanding cases in the magistrates courts falling, and in the crown court the backlog stabilising.”