British airlines on Sunday stepped up restrictions on suspected swine flu carriers, as a report said four more British students quarantined in China have had infections confirmed.
Britain is Europe's worst-hit territory, with estimates of 55,000 new cases last week, and both British Airways and Virgin Atlantic said they have put in place measures to turn back passengers showing symptoms.
"If we have concerns about a customer or the customer is concerned, then we have a 24-hour medical service we can call to give advice to staff," said a British Airways spokeswoman.
"There have been a number of cases where we have advised customers not to fly on the basis of their diagnosis or symptoms of H1N1."
Britain's health authorities are advising people with symptoms to delay journeys if they are feeling unwell.
"If there are signs of something being wrong, be it excessive sneezing or coughing, not looking well, high temperature, then the airport staff can call in a medical team for extra advice," added Virgin Atlantic spokesman Paul Charles.
"If the medical team believe there are reasons not to fly, the passenger will be asked to produce a fit to fly certificate from their doctor or a hospital, and they will be put at our cost on to the next available flight."
The news of more stringent checks came with a group of 52 students and teachers in quarantine after the British Council said four students tested positive for the A(H1N1) virus upon their arrival in Beijing for a study tour.