Every doctor and nurse in the country will have to submit to criminal record checks or be fined up to £5,000 because they fall under the scope of the government's Vetting and Barring Scheme.
The idea is to stop paedophiles getting into jobs with access to children and vulnerable adults.
Anyone who fails to register on the scheme administered by the Independent Safeguarding Authority will face criminal prosecution and a court fine.
To enforce this register of an estimated 11.3 million people in England, Wales and Northern Ireland, regular monitoring will take place and people could be banned from the list if new evidence is disclosed.
Anyone who works regularly with children or vulnerable adults, such as medical staff, teachers, dentists, prison officers and all 300,000 school governors will have to register on the scheme, which was recommended in the aftermath of the Soham murders, when Holly Wells and Jessica Chapman were killed by their school caretaker, Ian Huntley.
Two hundred case workers will decide who is barred after collecting information from police, employers and professional bodies.
To prevent another Huntley, who had no criminal record, officials can bar those with "soft intelligence" against them.
It is estimated that 40,000 people, double the current number, will be banned once the scheme is up and running. Criminal penalties, including jail terms, for employers giving sensitive jobs to those who are already barred, come into force next month.