By Juliet Bremner: ITV News correspondent

An operation involving 45 police forces has led to the arrest of 660 suspected paedophiles in the UK.

More than 400 children were protected as a result of the unprecedented six month operation run by the Nation Crime Agency.

The operation targeted people accessing indecent images of children online.

Of the people arrested, 39 were already on the register of sex offenders but the vast majority were not previously known to the law enforcement agencies.

It has not yet been decided how many of those arrested will be charged.

NCA officers say they have Credit: PA

Among those arrested during the operation are a doctor who allegedly had access to more than one million indecent images of children.

There is evidence that he had been communicating and meeting with young boys.

Another was a foster carer who had no previous convictions but was caring for a vulnerable child when he was arrested.

A grandfather who had access to 17 grandchildren - two of whom had previously reported his abuse - has been arrested.

One suspect admitted in interview that he'd been viewing images of children for over 30 years and travelling to Vietnam, Cambodia and Thailand for sexual purposes.

One suspect confessed that he had been viewing online images that had been filmed by another member of the group which showed him abusing a child in the most severe form of abuse.

The NCA will not say how they investigated or caught these suspects because they believe revealing the methods would allow some paedophiles to avoid detection.