Doctors are facing tough language checks which mean they cannot practice in the UK without a firm grasp of English.
A change to the law comes into effect today which means that medics licensed to practice in the UK can have their language skills checked by the General Medical Council (GMC).
The doctors' regulator hailed the change as a "milestone" for patient safety. Until now only doctors from outside Europe could have their language skills tested by the GMC, but this has been extended to doctors coming to Britain from inside Europe.
Niall Dickson, chief executive of the GMC, said: "This is an important milestone in creating better, safer care for patients. Everyone has a right to expect to be treated by doctors who can communicate effectively in English and this will help us achieve this.
"It is also important that everyone understands this does not in any way absolve those who employ doctors of their responsibilities - they must carry out thorough pre-employment checks and make sure that the doctor is qualified and competent to carry out the duties they are being given.
"This is not about singling out those doctors who have been trained outside the UK. They have made and are making an invaluable contribution to healthcare in the UK, but we cannot and will not tolerate doctors who cannot communicate clearly with patients and their colleagues - that is a basic component of safe, effective practice."
Health minister Dan Poulter said: "For the first time ever, we have a full system of checks in place to prevent doctors working in the NHS who do not have the necessary knowledge of English from treating patients. This is a huge step forward for patient safety."