Children suffering anxiety, depression and other low-level mental health conditions face a postcode lottery when seeking treatment, research has shown.

There are wide disparities in spending per child in different parts of England with more than a third of areas seeing a real-terms fall in spending on these services. This is despite soaring demand and increased government funding for children’s mental health nationally, the study by the children’s commissioner for England found.

Experts said early intervention by school nurses, counsellors, drop-in centres or online support services to address low-level conditions can prevent them developing into more serious illnesses. And the report warned children may be losing out at this crucial point.

Researchers used spending data from local authorities and NHS clinical commissioning groups, which each contribute roughly half of funding, to calculate that local areas allocated £226m for low-level mental health services in 2018-19 – just over £14 per child.

But while local authority spending per child in London was £17.88, it was just £5.32 in the east of England. According to the study, a few very high-spending areas mask a larger proportion of low-spending areas.

The report’s findings showed the top 25% of local areas each spent upwards of £1.1m while the bottom 25% spent £177,000 or less. Spending per child was higher in London and the north-east, lower in the East Midlands, east of England and south-east. Urban areas were slightly better off than rural regions.

The total reported spend across all areas increased by 17% in real terms between 2016-17 and 2018-19. While most areas (58%) enjoyed a real-terms increase in spend per child over the same period, more than a third of areas (37%) saw a real-terms fall, often because of reduced local authority investment.

Anne Longfield, the children’s commissioner for England, said: “It is extremely worrying that a third of local areas in England are actually reducing real-terms spending on these vital services.

“The children I speak to who are suffering from conditions like anxiety and depression aren’t asking for intensive in-patient therapeutic treatment, they just want to be able to talk to a counsellor about their worries and to be offered advice on how to stop their problems turning into a crisis.

“The NHS 10-year plan has made children’s mental health a top priority, but it won’t succeed unless children with low-level mental health problems are offered help quickly and early.”

Longfield acknowledged the financial pressures on local authorities, whose budgets have been slashed by government austerity policies, but added: “Those who are spending barely anything on low-level mental health cannot continue to leave children to struggle alone.”

Chair of the Local Government Association’s children and young people board, Anntoinette Bramble, said: “Children’s services face a funding gap of £3.1bn by 2025 while public health services, which also help children get the best start in life, have seen cuts of £700m. If we are to improve provision of preventative and early-intervention services then it is vital the government adequately funds these in the forthcoming spending review.”

A Department of Health and Social Care spokesperson said investing in children’s mental health was a priority for government. “We are transforming services through the NHS long-term plan – backed by an extra £2.3bn a year – so that 70,000 more children a year have access to specialist mental health care by 2020-21.

“Early intervention is vital and we’re going further, piloting a four-week waiting time standard for treatment, training a brand new dedicated mental health workforce for schools across the country, and teaching pupils what good mental and physical health looks like.”