Table 1 The four simulation scenarios considered in this study (two baseline scenarios and two intervention scenarios)

Baseline A: based on Tojesen [21]

This scenario predicted a doubling in demand from April 2021 for GPs, crisis and inpatient levels 2, 3 and 5, followed by drop to pre pandemic levels in Oct 2021. In addition, IAPT Assessment will experience a decrease in demand of 20% in April 2021 and a subsequent increase of 25% from April 2022, before returning to pre pandemic levels in Oct 2022

Intervention A involved increasing capacity in GP primary care (Level 2) by 30%, as well as reducing length of stay in IAPT therapy (level 3) by 20%

Baseline B: based on Hood et al. [22]

The NHS-based Strategy Unit predicted that demand for primary mental health (IAPT, GP, primary mental health team) will increase by 22% in 2020/2021, by 20% in 2021/2022 and by 12% in 2022/2023 compared to before the pandemic. Secondary care service will experience a 25% increase in demand in 2020/2021, 24% in 2021/2022 and 14% in 2022/2023. Whereas the secondary care crisis service will have a 13% increase in demand estimated in 2020/2021, 12% in 2021/2022 and a 7% in 2022/2023. Finally, specialist inpatient will experience a small increase of 1% in 2021/2022 and none by 2022/2023

Intervention B extended Intervention A by: increasing capacity at community general and specialist (level 4) by 20% and 30% respectively; reducing of length of stay in community specialist by 70 weeks instead of 78 weeks; increasing flow rates from community specialist care (Level 4) to general mental health services and crisis (Level 4) by 30%