Doctors are required to meet clinical standards and have kept up to date with medical advances under a wave of new skills checks.
Described as "the biggest change in medical regulation for more than 150 years", the so-called revalidation process is intended to reach all 230,000 of the UK's licensed doctors.
At present, doctors can go for their entire careers without facing any formal assessment of their competency. But under radical plans coming into force from Monday, doctors will be assessed to see if they are fit to stay on the medical register.
The UK is the first country in the world to introduce such a system across its whole healthcare system, covering GPs, hospital doctors, locums and those working in the independent sector.
Health Minister Dr Dan Poulter said: "Today is a momentous day - as doctors in the UK become the first in the world to have regular assessments to ensure that their training and expertise are up to date and that they remain fit to carry out their important role of providing high quality care for patients."
The new system will mean that problems with doctors are flagged earlier, said the General Medical Council (GMC). The assessment will take the form of an annual appraisal - featuring input from patients - and a more comprehensive meeting every five years.
Health officials have been considering revalidation for many years. The GMC began creating a revalidation model after the 2001 public inquiry into failings in the children's heart surgery service at Bristol Royal Infirmary. But the 2005 Shipman Inquiry, which looked into the case of serial killer and GP Harold Shipman, was heavily critical of the initial proposals so health officials created a new model and organised pilots.
In one pilot study, conducted on 3,000 doctors, concerns were raised about 1% of the medics. Another survey of 320 of the designated bodies in England found concerns about 4.1% of doctors. Worries raised ranged from tardiness to more serious concerns about clinical competency.
The GMC described the shake-up as "the biggest change in medical regulation for more than 150 years".
It added: "Revalidation is not a panacea, it is not a magic bullet to guarantee that care is safe or that every doctor is perfect, it will take time to settle in, we will need to evaluate and improve the model."