Boots is to offer individual lateral flow tests for as much as £5.99, including delivery, from Wednesday as retailers gear up for the end of widely available free tests.

The UK’s biggest pharmacy business said customers would be able to order one test online from Wednesday or pay £17 for a pack of four, including delivery within two days. These tests will include the option to send results to the UK Health Security Agency (UKHSA) but they cannot be used for travel requiring a negative antigen test certificate.

From early March, Boots said it would be possible to pick up lateral flow tests in more than 400 of its stores for £2.50 for one or £12 for a pack of five. These cheaper tests will also be available online with four tests priced at £9.50. These tests don’t have the UKHSA reporting function.

Dan Shears, national health and safety director at the GMB union, said: “This is rampant profiteering at the expense of working people. Almost £6 per test is a huge sacrifice for the lowest paid workers, and, if they wish to test family members as well, then the cost will soon become prohibitive.

“The government should provide tests for free – they are a clear public health benefit that far outweighs cost. But if we have to pay, test provision should be subsidised to make tests affordable.

“The reality is that those who are most at risk are least able to afford testing, meaning it will not happen and low-paid workers – many of whom are key workers – will continue to take the brunt of Covid.”

Frances O’Grady, general secretary of the TUC union body, agreed that free tests must remain in place. She said: “Introducing charges for Covid tests in the middle of a cost-of-living crisis is both heartless and reckless. This decision will hit low-income and frontline workers the hardest – at a time when many are struggling to make ends meet. Do ministers really want low-paid staff – with public-facing jobs – to go into work untested?”

Asif Aziz, director of healthcare services at Boots UK, said: “We are pleased to be expanding our Covid-19 testing services even further, with affordable lateral flow testing options for those who still want peace of mind from asymptomatic testing.

“While it is great that we are returning to normal and finding a way to live with Covid-19, we encourage our customers and patients to stay safe and continue to take measures to limit the spread of the virus, especially to those in vulnerable groups.”

Free testing for the general public will end in England from 1 April, with most people having to pay for lateral flow and PCR tests including those visiting people in care homes. There will be some exceptions. Free symptomatic tests will continue to be available for NHS patients and those in care homes, and some asymptomatic testing for both.

More broadly, the UKHSA has yet to set out which other groups will remain eligible for free tests, although availability is expected to be limited to people aged 80 and above or those with compromised immune systems only. There will also be tests kept for the Panoramic study, which is assessing the efficacy of antiviral drugs, the Vivaldi scheme, examining Covid in care homes, and Siren, which looks at the NHS.

Announcing the change of plan on Monday, the prime minister, Boris Johnson, emphasised “personal responsibility” as the best way to control Covid-19 from now on. Johnson said the primary line of defence would be “pharmaceutical interventions”, such as antivirals and vaccines.

However, concerns have been raised about testing for NHS staff and other workers dealing regularly with the general public.

The British Independent Retailers Association, which represents thousands of small local shops, said it was concerned about the end of free testing. “Employers have a duty of care and need to know if they are required to provide testing facilities to employees – if yes then the kits should be free to employers,” said Andrew Goodacre, the chief executive of the trade body.