NHS Scotland is “seriously struggling to become financially sustainable”, doctors’ leaders have warned – as a new report suggests it may face a £1.8 billion shortfall within four years.

Watchdog Audit Scotland says the gap may emerge within the funding of social care by 2023-24 unless changes are made.

Auditor General Caroline Gardner said: “The NHS in Scotland is running too hot, with intense pressure on staff and a service model that will remain financially unsustainable without a much greater focus on health and social care integration.”

The warning comes as the NHS in Scotland faces a “significant” maintenance backlog and challenges resulting from Brexit, while only two out of eight key national waiting times standards are being met.

In addition, Audit Scotland said Scottish Government plans to provide more care closer to home and cut hospital demand “will not be achieved by 2020”.

Without reform, the report said ministers have already forecast spending on health and social care could rise to £20.6bn by 2023-24 – up from £13.4bn in the 2018-19 budget.

The NHS budget deficit is also expected to reach £207million in 2021-21.

Responding, BMA Scotland chairman Dr Lewis Morrison said the report “paints a stark picture of the parlous state of our NHS”. He said: “It is clear our NHS is seriously struggling to become financially sustainable.

“The suggestion of a £1.8bn funding gap for 2023- 24 – something we have been warning of for some time – just serves to illustrate the growing gap between demand for care and resources available to our NHS.

“On top of this, there remains a lack of a clear plan on how to address this funding gap that is clearly developing, or set out the reforms needed to prevent it developing in the first place.”

National performance declined for six out of the eight standards in 2018-19, the Audit Scotland report said.

Health Secretary Jeane Freeman said the report noted “positive steps” while recognising challenges over demand and staffing.

The minister said: “As recognised by Audit Scotland, investment in our health services has grown by 6% above inflation over the last 10 years, and now exceeds £14bn this year. This is all part of our twin approach of investment and reform to meet increasing demand and to deliver balanced and sustainable services.”

But LibDem health spokesman Alex Cole-Hamilton was unconvinced, saying: “The SNP have been in charge of safeguarding our NHS for more than a decade and have shown themselves to be incapable of dealing with the day-to-day, let-alone the long-term reforms.”

And Labour’s Jenny Marra, convener of the Public Audit and Post-Legislative Scrutiny Committee, said: “Last year’s report from the Auditor General said NHS Scotland’s position was not financially sustainable, and now we see the NHS deficit spiralling. The Audit Committee will be prioritising our scrutiny of this report to understand more fully how the Scottish Government and health boards plan to tackle the £200m plus deficit predicted for 2021-22.”

Meanwhile, Alison Johnstone of the Greens called for a review of GP recruitment, resources and funding, as backed by parliament when Johnstone brought a motion on the subject in April.

She said: “General practice carries out the majority of patient contact in Scotland, yet it has been receiving a declining share of NHS spend since 2005-06.”