Pandemic flu service to go live
The National Flu Service is expected to go live later, giving thousands of swine flu sufferers access to drugs without needing to consult with a GP.
The phone and website service, which will only cover England, is the first of its kind in the world.
It has been designed to relieve pressure on the NHS and will use a checklist to diagnoses cases.
Pregnant women, people with health conditions and the under-ones will still all be referred to GPs.
The Department of Health has accepted that the service could be abused with people giving the answers they believe will give them access to anti-flu drugs.
But Chief Medical Officer Sir Liam Donaldson has said it was a price worth paying to help the NHS cope with its "biggest challenge in a generation".
He told the BBC this week that the flu service may just be the first step in how the health service responds to a pandemic which has already claimed more than 700 lives across the world.
The death toll in the UK stands at 31, but that is likely to climb when the Department of Health in England releases its weekly update on Thursday.
Under contingency plans, non-emergency operations can be cancelled, while doctors can be moved around the health service to help flu hotspots cope.
It will be staffed by 1,500 call handlers to start with, although there is already capacity for 2,000 people in the network of call centres.
The free-phone number will only be operational during the day, but officials stressed that it will expand to meet the requirements of the pandemic.
BBC health correspondent Jane Dreaper said: "Officials are anxious to make sure that the service is thoroughly tested as an overloaded website or blocked telephone lines would prove highly embarrassing."
The launch of the service was announced last week after GPs and NHS Direct reported a dramatic rise in calls and consultations.
Every region of England is now seeing "exceptional" levels of activity with the exception of Yorkshire and the Humber.
And a poll of 1,500 NHS staff by the Health Service Journal and Nursing Times showed 14% did not think their organisation was coping successfully with the pressure.
The flu service is not covering the rest of the UK as Wales, Northern Ireland and Scotland have all experienced much less demand. They will be able to plug into it if and when they need to.
Dr Richard Vautrey, of the British Medical Association, which has helped to design the checklist being used by the flu service, said: "What we have to remember is that this is a unique situation.
"Some GP practices are receiving hundreds of calls a day and we have to prioritise so we can see the most seriously ill.
"It has been designed by doctors to pick up problems that need to be seen by someone with a medical background.
"So as long as the call handlers get the correct training we can be confident in this service."