Funding for this research was provided by:
The Health Foundation
Received: 10 September 2019
Accepted: 29 November 2019
First Online: 27 December 2019
Ethics approval and consent to participate
: This study was considered by the Chair of the UCL Research Ethics Committee on 29 February 2016 and is exempt from the requirement to obtain ethical approval.
: Not applicable.
: The corresponding author is an editorial board member of BMC Health Services Research.