A poultry worker travelled to Scotland when they were positive with bird flu - risking a "disastrous" new pandemic.
The bird flu containment strategy has been slammed today, following the development the worker made the journey while awaiting test results.
They travelled from their address to a location in Scotland, though the exact destination has yet to be disclosed.
Experts say this could have pawned a "potential disaster" and called for workers to self-isolate until swabs are confirmed negative in future.
John Fulton, a pharmaceutical industry consultant and founder of BioNiagara, said: "Any workers... should err on the side of extreme caution until their test results are in by isolating."
"Covid started with one case in Wuhan.
"[Bird flu's] capacity of human-to-human spread is getting more probable. Pandemics emerge almost from nowhere, randomly and under a blue sky."
But no new cases have been spotted, and health chiefs are confident anyone potentially at risk has already been hunted down.
There is also no proof human-to-human transmission has occurred yet, a hurdle that has so far stopped bird flu from triggering a Covid-style crisis.
Mr Fulton told MailOnline authorities should take every precaution available at the moment.
Only two bird flu control zones were enforced in England at the time of the infection, one in Cantley, South Yorkshire and another in Scunthorpe, Lincolnshire.
Once the outbreak in animals at the farm the two worked at was detected, all birds were culled. A 3km protection zone was also enforced, restricting the movement of all poultry in efforts to contain any further spread.
All workers potentially exposed to the virus were asked to take a Covid-style test for the virus, as per official protocol.
No restrictions were imposed on their movement while they awaited the results.
Swabs were sent to a special laboratory, in a process that can take several days.
Under current rules, anyone potentially exposed in such situations are also asked to call health officials if they develop any flu-like symptoms over the next 10 days.
Public Health Scotland said the worker was only in the country "briefly" for a few days and that contract tracing of people they met on their trip had returned no further positive tests for bird flu.
Local public health teams are in contact with people who have been in contact with avian flu, as protocol. UK Health Security Agency says these workers voluntarily took part in an asymptomatic study, and had no symptoms of bird flu at the time.
