People could be refusing to get tested for coronavirus in a bid to avoid having to self-isolate, a Government adviser has said.

Professor Robert West, a member of the Scientific Pandemic Influenza Group on Behaviours (Spi-B), which advises ministers, said it could be a factor in the difference between the high infection rate in the UK and the decrease in daily positive cases.

The latest estimates from the Office for National Statistics (ONS) show that Covid infections are up to their highest level since January in England, and the highest since February in Wales.

The ONS’s household swab test survey showed that around one in 65 people in private households in England had Covid-19 in the week to July 24 – up from one in 75 in the previous week, and the ninth consecutive week that infections have increased.

Infections are also estimated to have risen in Northern Ireland, though numbers have dropped in Scotland.

In contrast, the Government’s daily testing figures show positive cases in the UK have fallen by 36% in the past seven days, with 29,622 laboratory-confirmed cases recorded on Friday.

As of 9am on Saturday, the Government said there had been a further 26,144 lab-confirmed cases in the UK.

Even after a lag in recording the ONS data had been accounted for, health psychologist Prof West said the discrepancy between the infection and case rate – the number of people testing positive for coronavirus each day – was a “puzzle”.

The University College London academic suggested people were reluctant to quarantine if they were found to have the infection, so they were boycotting tests.

Prof West told BBC Radio 4’s Today programme: “One of the things that is a concern is that people may not be coming forward as they used to do for testing.

“One of the reasons for that may be that the messaging from the Government in a way has sort of given a bit of a green light to people to say, ‘well, it is not so bad if you get the infection’.

“(But) if you get tested you’re going to have to self-isolate, at least at the moment, and that’s going to be very disruptive. I suspect that may be a factor.”

The ONS survey provides a snapshot of the prevalence of Covid-19 across the UK, and estimates the percentage of people who are likely to test positive at any point in time.

It takes time to collate as it is based on a sample of swab tests collected from households across the UK, so there is a lag in reporting the data against the Government’s daily testing figures.

Prof West’s theory came after Labour launched a fresh offensive on Friday calling for the Prime Minister to bring forward the date when people who have been fully vaccinated can skip self-isolation.

Boris Johnson said the August 16 date was “nailed on”, but opposition leader Sir Keir Starmer is pushing for the Government to follow Welsh Labour’s lead, with First Minister Mark Drakeford affording extra freedoms for the double-jabbed by August 7.

The so-called “pingdemic” has caused disruption to several sectors, with record numbers being alerted by the NHS Covid-19 app to self-isolate in recent weeks, including 700,000 for the week to July 21.

The Government has responded by rolling out exemptions for workers it deems to be employed in critical industries, such as those in the food sector, along with transport, waste collection and defence staff.

Daily negative test results can enable such workers who have been alerted by the NHS Covid-19 app or called by NHS Test and Trace as coronavirus contacts to continue working.

A row is also brewing over so-called vaccine passports with critics ramping up pressure for Parliament to be recalled from its summer break over suggestions people could be forced to show proof of being double jabbed to gain entry to venues and events in Britain.

Liberal Democrat leader Sir Ed Davey, who is leading the charge for MPs to return, accused the Government of trying to bring vaccine passports in by “stealth” after a change was rolled out to the NHS app allowing users to prove their vaccine status in domestic settings, as well as for international travel.

“They are trying to do this in the recess when Parliament isn’t sitting – it is a disgrace,” the former cabinet minister told Times Radio.

“It is an abuse of democracy, it is an abuse of power and it threatens taking people’s freedoms away and stigmatising young people, hitting businesses – that is not acceptable.”

But Damian Collins, Conservative MP and former chair of the Digital, Culture, Media and Sport Select Committee, said those who had chosen not to get vaccinated could not expect “to be treated in the same way” as those who had, especially when venue owners may want increased guarantees to satisfy their insurance.

Although more than 70% of adults in the UK have now been double jabbed, people will continue to be encouraged to get inoculated at mass events this weekend.

Visitors to the Circus Extreme in Halifax, Yorkshire, on Saturday will be able to grab a shot, with a pop-up clinic will be just outside the Big Top so even people who do not have tickets to the show will still be able to get their vaccine.

Football fans can get vaccinated at Burnley FC, where a pop-up site will be administering doses of Pfizer, while jabs will be on offer on Saturday at Goodwood Racecourse near Chichester.

In west London, a vaccine bus will be stationed at the Summer of Love Festival in Holland Park, while in the east of the city a four-day vaccine festival is running in Poplar until Monday, with live music and free food.

Meanwhile, Government data showed a further 71 people had died within 28 days of testing positive for Covid-19 as of Saturday, bringing the UK total to 129,654.

Separate figures published by the Office for National Statistics show there have been 154,000 deaths registered in the UK where Covid-19 was mentioned on the death certificate.