Two mothers have said they were able to book Covid-19 tests in Nottingham by using a Scottish postcode.
Tina Eaton, from Beeston, drove to the mobile test centre after struggling to book an appointment for her son through the online system.
Staff there told her booking an appointment in Scotland would generate a QR code that could be used to take a test in Nottingham.
The government said it was working to close the loophole.
Both women said they had been unable to secure slots at the Motorpoint Arena test centre in Nottingham city centre.
of people just turning up and I thought, ‘What have I got to lose?’
“The guys on the gate asked for a QR code and when I said I couldn’t get through they said pull over and type in a Scottish postcode and that will give you a QR code.
“I was quite panicky because I didn’t want to take somebody else’s slot in Scotland but they said it was fine.”
Another mother, Sara, said her two daughters developed coughs over the weekend and weren’t allowed to go back to school until they had a negative Covid-19 test.
She was also tipped off by staff at the Serco-run test centre to book a slot “anywhere in Scotland”.
“I felt like it was a bit wrong because I would be taking a test opportunity from someone else but I got a QR code for Glasgow and sure enough they let me in,” she said.
The Department of Health and Social Care said: “Using incorrect postcodes to get a test is not permitted and testing sites should not process appointments that have been allocated to different sites.”
It added the issue was being resolved and testing sites were being reminded of the correct booking process.
A Serco spokesman said: “All our teams are required to follow DHSC instructions and procedures, including only accepting the correct QR codes.”
Follow BBC East Midlands on Facebook, Twitter, or Instagram. Send your story ideas to email@example.com.