A mental health trust has had to put more than half a million pounds extra into a “one stop” service for children and young people after referrals were close to double the expected levels.

The Mindsight children and adolescent mental health service run by Surrey and Borders Partnership Foundation Trust is jointly commissioned by the area’s clinical commissioning groups and Surrey County Council. It aims to provide a “no wrong door” approach so no patient is excluded.

The trust, which has so far absorbed the £664,000 overspend on the fixed £13m contract, has now warned the current model is unsustainable. It said referral criteria will have to change, the service remodelled or additional money will be needed to deliver it.

Referrals have soared since the service was launched in April 2016. The trust saw 11,500 referrals in 2017-18, rather than the 6,545 referrals covered in the contract. This has led to more than 2,000 young people waiting for assessment or treatment, huge caseloads for healthcare professionals – one non-medical prescriber is responsible for 287 patients – and waiting times for routine appointments up to 19 months.

The trust has had to take emergency measures to ensure children are not put at risk. Telephone calls with young people and their families identify any concerns and clinicians review their caseloads to identify patients who need a face to face harm review. However, this means some routine appointments are having to be rescheduled.

The trust is working with commissioners to agree an independent review that will make recommendations about a sustainable service. It has also proposed an interim “slow down” where referral criteria for some groups would change, reducing referrals and allowing clinicians to assess existing referrals and start treatment.

An interim plan being developed includes alternative routes and capacity for a limited period, developing referral criteria and assessment thresholds, and a pre-referral support package for schools and GPs. This will be discussed by the trust board today.