Footnotes

• Contributors AJP and DG conceived the manuscript. AJP wrote the first draft. All authors contributed to development of the idea and ongoing writing, and approved the final manuscript.

• Funding This article presents independent research commissioned by the National Institute for Health Research (NIHR) under the Collaborations for Leadership in Applied Health Research and Care (CLAHRC) programme for North West London. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.

• Competing interests None declared.

• Provenance and peer review Not commissioned; externally peer reviewed.