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.
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.