The UK’s test and trace programme buckled under the pressure of the coronavirus second wave over winter, according to a report by the national spending watchdog that warns the system was still blighted by poor performance in April when infection rates were down sharply from the peak.

The National Audit Office said NHS Test & Trace’s performance “fell well below its targets when cases rose sharply in December.”

When the second wave took hold at the end of last year, instead of turning round all gold standard PCR test results within 24 hours as promised by prime minister Boris Johnson, it was returning just 17 per cent. This figure had recovered to 90 per cent by April, as demand for testing dropped with daily cases running at a few thousand a day, down from a peak of nearly 70,000 daily cases in January.

Yet targets on test turnround times as well as on contact tracing were still not met during some weeks in April, the NAO found. “[Test and Trace] has further to go in reducing the overall time taken for reaching all cases and their contacts,” it said.

The report, which focuses on the period between November and April, found that during that time just 57 per cent of test results were returned within 24 hours.

The report also questioned the effectiveness of the mass testing programme for people without symptoms, highlighting the low proportion of rapid Covid-19 tests that have been registered as used.

The self-testing kits, designed to allow a return to classrooms and easing of other restrictions, were rolled out in October but by the end of May only 96m results out of the 691m lateral flow tests distributed were logged on the system.

Infections are beginning to surge once again across the UK. On Thursday, 16,703 Covid-19 cases were reported, the highest daily figure since early February.

Meg Hillier, chair of the public accounts committee, said the programme “must urgently improve” to deliver an effective service, adding it needed to “get to grips with some fundamental parts of the process, such as its timeliness in reaching contacts for all the tests it provides, people coming forward for tests when they have symptoms, and compliance with self-isolation”.

The timeframe of the highly critical report, the second by the NAO, covers the last six months of Lady Dido Harding’s tenure as head of the programme, which has faced heavy criticism since it was set up last May. Harding, who did not respond to a request for comment, recently announced her candidacy to become the next boss of NHS England.

The watchdog was critical of NHS Test & Trace management for its failure to “reduce its dependency” on management consultants despite pledging to do so. Consultants made up nearly half of the workforce by April this year, with the number increasingly slightly since December to about 2,200.

The NAO also found “low or variable” levels of compliance with the contact tracing system. It added that while collaboration with local authorities had “improved”, local contact tracing teams “cannot yet access all the data they need”.

Gareth Davies, head of the NAO, acknowledged the programme had made “a lot of changes” since winter, including the introduction of mass asymptomatic testing and surge testing to limit the spread of variants, but he said there were still faults with the system.

“Some pressing challenges need to be tackled if [NHS Test & Trace] is to achieve its objectives and deliver value for taxpayers, including understanding how many lateral flow devices are actually being used and increasing public compliance with testing and self-isolation,” he said.

The report noted that NHS Test & Trace had only spent three-fifths of its £22.2bn annual budget, but that it was still wasting money on call centre capacity “it does not use”.

The watchdog also warned there was a risk that the continuing integration of the programme into the new UK Health Security Agency would “divert NHS T & T’s attention away from efforts to contain the spread of the virus”.

The government said: “The testing and tracing being delivered across the country is saving lives every single day and helping us send this virus into retreat by breaking chains of transmission and spotting outbreaks wherever they exist.”