By Clare Murphy
BBC News health reporter
There have been been reports of lenthy waits and recorded messages
Many people concerned about swine flu have turned to NHS Direct for help, but the telephone helpline which is supposed to take the pressure off doctors is now trying to take the pressure off itself.
The service, set up in 1997, has long been a target for criticism from doctors who have attacked what they see as its over-cautiousness.
Designed to take the strain off frontline staff, some claim it has increased workloads in the past by referring the perfectly healthy to out-of-hour doctors or A&E.
But many value its reassurance and advice and have turned to it in droves since swine flu was first reported. On Tuesday it received more than 9,000 calls relating to the virus - the highest yet.
There have been reports of lengthy waits to speak to an advisor - if you get through. Others have simply heard a recorded message.
One of the problems is that hundreds of fundamentally well people are still calling the service with their questions about swine flu, despite there being another telephone number for this purpose.
Many others have little wrong with them and are offered advice about home care.
NHS Direct itself is now urging people to use other channels for information, notably the symptom checker on www.nhs.uk.
But the swine flu expert at the British Medical Association - the doctors's union - said the service was still not effectively triaging, and that too many were being referred to their GPs.
"NHS Direct has a place in the ordinary run of things but it is not tooled up for this job and it is struggling with the volume of calls," says Dr Peter Holden.
"As a working GP dealing with possible cases of swine flu NHS Direct has made no difference to my work load and has even made it harder, as I am getting a lot of referrals late in the day."
Those with children under five are specifically advised not to use the symptom checker on the NHS Direct website and contact the service directly.
Amanda McGregor, a mother of a one-year-old, said she decided to ring NHS Direct for advice and reassurance about her son's high temperature.
"My husband and I couldn't believe it when we got an answerphone saying they could not take calls because they had such a high volume of people ringing about swine flu. A voice message said information was available online."
"We ended up phoning our after hours GP service and were told to bring our toddler in. We were then transferred to accident and emergency and prescribed Tamiflu."
A fever is the most important symptom of swine flu - that is a temperature of 38C (100.4F) and over. Then there are other symptoms such as a cough, runny nose, sore throat or chills.
There is reportedly little standard seasonal flu at the moment, so the chances are that if you have a fever and other symptoms you do indeed have swine flu, experts say.
"Basically go out and buy a thermometer. If you have a temperature and two of the other symptoms you have flu, and should get treatment. If you're well enough to go to work, you don't," says Dr Holden.
On Tuesday NHS Direct received nearly 9,700 swine flu related calls and its chief executive said it was now encouraging people to use other means of obtaining information.
But Nick Chapman, chief executive of NHS Direct, stressed it was not simply referring callers straight on to GPs as some have claimed, and was sorting out the mildly ill from potential cases of swine flu.
"I am extremely aware of the current pressures facing all parts of the NHS, including GPs, and want to reassure people that NHS Direct is doing all it can to help relieve this pressure. We are dealing with a significantly increased number of calls about swine flu, yesterday alone nurses spoke to over 9,500 people who were worried they had swine flu.
"For half of these people we were able to give advice on how they could treat themselves at home, without advising them to contact their GP for further assessment.
"We are prioritising urgent calls so that people most in need are assessed as quickly as possible and urgent calls are being dealt with in less than 20 minutes. If a call back is required for a non-urgent call we will tell callers how long they have to wait when they speak to someone."