The government has written to directors of children’s services across England urging them to prioritise adoption for children in the care system and to ensure that prospective adopters are not turned away when they are actually eligible.

Ministers say they want a renewed focus on adoption from all local authorities and have called on councils to review their practices following a drop in the number of assessments recommending adoption as the best option for a vulnerable child.

Figures published by the Department for Education (DfE) last month revealed the number of adoptions in England has fallen by a third in the past four years, dropping to 3,570 in the year up to the end of March 2018 from a peak of 5,360 in 2015.

The education secretary, Gavin Williamson, said if councils believed adoption was in the best interests of a child he would back them 100%. “Adoption can transform the lives of children waiting in care for a permanent, loving home,” he said.

The government intervention was welcomed by Adoption UK, the national charity for adopters, but others in the sector expressed dismay at what one described as the government’s “unthinking devotion to adoption” while neglecting other forms of care including kinship care, where a child is cared for by relatives.

Critics say only a small minority of children in the care system are suitable for adoption, yet adoption appears once again to be at the top of a hierarchy of care. Other political leaders including Tony Blair, Michael Gove and David Cameron have all previously sought to increase adoption rates and improve services.

As part of its latest adoption push, the DfE has published new advice for councils, clarifying that age, income, sexual orientation and marital status should not be used as reasons to reject prospective adopters.

The letter to children’s services directors from Michelle Donelan, the minister for children and families, also states that agencies should not prioritise trying to find the “perfect” ethnic match. The latest data shows that of the 2,700 children waiting for adoption, almost 40% have waited over 18 months. Of these, 24% were from BAME backgrounds.

“Children’s needs should be at the forefront of decisions,” she writes. “I urge you not to shy away from putting children forward for adoption where you think it would be in their best interests.”

Andy Elvin, the chief executive of the Adolescent and Children’s Trust, the UK’s largest fostering and adoption charity, said: “I had hoped that politicians had moved beyond this insulting language and unthinking devotion to adoption.

“Children in foster care are not ‘waiting for a permanent, loving home’: they are living in one. Long-term stability is vital and it is achieved in different ways for different children.

“For some it is returning to birth parents, for some it is going to live with a relative who has selflessly come forward, for some it is long-term foster care, for some it is residential care and for some it is adoption. There is no hierarchy to these options, it depends on the individual child’s circumstance.”

Cathy Ashley, the chief executive of Family Rights Group, added: “Adoption is the right solution for some children. However, far more children who cannot live with their parents flourish in the care of wider family, yet the latter receives negligible recognition, support or finance.”

Sue Armstrong-Brown, the chief executive of Adoption UK, welcomed the government’s renewed commitment to adoption. “This means investing to value adopters and the love and stability they provide for the most complex and vulnerable children in society.”