Unmarried and same-sex couples are now legally allowed to adopt together under a new law.

In one of the most significant changes in modern adoption history, both adults can become a child's adoptive parents.

Previously, only married couples or single people could apply.

The Adoption and Children Act became law on December 30, three years after it was passed by Parliament.

The British Association for Adoption and Fostering (BAAF) has hailed the act as "the most radical overhaul of adoption law for 30 years".

Chief executive Felicity Collier said: "These changes will have a major impact on thousands of families. We know there were people eagerly awaiting December 30 because they are an unmarried couple who would like to adopt jointly. Opening up adoption to unmarried partners will encourage more people to consider adoption.

"This is very important at a time when too many children wait too long in temporary care for an adoptive family or, in some cases, never have the chance of adoption at all."

The new act also introduces special guardianship orders that give foster carers, relatives and others caring for a child, the opportunity to apply for a special guardianship order which is expected to last until the child is 18.

This will mean the child is no longer the responsibility of the local authority.

Other changes include giving birth mothers and other birth relatives the right to ask for an intermediary service to trace an adopted child years later and find out if contact would be welcome.