The Home Office collects and publishes information on the primary roles that police officers perform, as well as the number of frontline officers, for every police force area in England and Wales. These data are published annually as part of the 'police workforce, England and Wales' statistical bulletin, the latest of which can be accessed here: https://www.gov.uk/government/statistics/police-workforce-england-and-wales-31-march-2017
Data on the primary roles officers perform, and the number of officers on the frontline, are collected at police force area level only, and cannot be broken down any further. Furthermore, the number of officers specifically on foot patrol cannot be separately identified in the data. The latest available data on frontline officers, broken down by police force area and going back to 2010, can be found in Table_F5 of the data tables accompanying the main release.
Data for the years 2010 to 2014 are estimated since data prior to 31 March 2015 were collected under a different framework, with different definitions.
Decisions on the size and deployment of the police workforce are operational matters for Chief Officers working with their Police and Crime Commissioners and taking into account local priorities.