GPs are required to issue patients with a new "fit note", replacing the previous "sick note", as of today (Tuesday 6 April 2010).
The single revised Statement of Fitness for Work replaces Forms Med 3 and Med 5.
The new form was developed in consultation with practising doctors, the Royal College of GPs and the British Medical Association.
The change was implemented by the Department of Work and Pensions as part of a drive to help people stay in work and reduce the estimated £100bn a year that sickness leave costs the economy.
Under the new scheme, a GP is able to say that their patient is either "unfit for work" or "may be fit for work".
In the latter case, the GP should go on to select from a non-exhaustive list of changes that they consider may assist their patient to return to work.
The BMA says that the fit note means the onus is now on employers to help get their staff back to work. Commenting on the change, Dr Laurence Buckman, Chairman of the BMA's GPs Committee, said: "Being in work is good for people's health and wellbeing and it's for that reason the BMA is pleased that the sick note system has finally been overhauled.
"It should reduce the number of forms used and will provide a better way for a GP to give advice about a patient to their employer."
He added: "From today the responsibility will be on employers to act: if a GP decides their patient is capable of some form of work, for example if they've got back pain and they should temporarily avoid elements of their normal job, then it will be down to the employer to be flexible enough to accommodate them.
"However, we think much more needs to be done to ensure employers, in particular local line managers, have enough information about the changes. Many may not realise, for example, there's no need to insist that an employee sees their GP simply to get signed back to work; in most cases that is not necessary.
"GPs also need to be careful they are not drawn into making comments they are not qualified to make, because, unlike occupational health doctors, they are not often in a position to know the details of the patient's working conditions, neither do they have specialist knowledge of workplace hazards.
"Employers have a responsibility to provide adequate occupational health services and the government must encourage them to provide that if the overall plan to help more people back to work is to be truly effective."