Background: Mental healthcare services for children and young people (CYP) are a very limited resource in the UK. To prevent health inequalities, measures to increase overall capacity must sit alongside measures that ensure utilisation matches need.

Aim: Our aim was to identify subgroups of CYP with unexpectedly low mental health service utilisation, presumably representing unmet need, and to assess whether there is area variation in the socioeconomic gradient of mental healthcare use.

Methods: This is a cross-sectional population survey of CYP (aged 5–24 years) using electronic health records from the Discover Now research platform, covering approximately 95% of the Northwest London resident population of 2.4 million people.

Results: The total sample comprised 764 327 CYP, of whom 2.1% attended a mental healthcare appointment in 2021 (95% CI 2.1% to 2.2%), our outcome measure. Lower socioeconomic status (our main exposure factor) was related to higher occurrence of mental healthcare appointments (+5% for each quintile increase in deprivation (95% CI 2% to 7%, p<0.001]). However, interaction analyses showed that the boroughs with unexpectedly low utilisation rates were also those not showing a clear trend between socioeconomic conditions and services utilisation (interaction p<0.001), suggesting that in these boroughs the occurrence of mental disorders in disadvantaged people was not captured by our analysis based on service utilisation. In some London boroughs, we found lower-than-expected activity for the most disadvantaged CYP.

Conclusions: The mental healthcare needs of many CYP from socioeconomically deprived areas of Northwest London may be unmet. More information is needed to confirm our results.