The Home Office does not maintain central records of an individual’s military career history. Providing the information requested would therefore require a manual check of individual records which could only be done at disproportionate cost.
The Home Office publishes data on returns from the UK in the ‘Immigration Statistics Quarterly Release’ (https://www.gov.uk/government/collections/immigration-statistics-quarterly-release). Data on the number of returns, by year, nationality and type of return are published in table Ret_D01 (https://www.gov.uk/government/statistical-data-sets/returns-and-detention-datasets) within the returns detailed dataset.
The term 'deportations' refers to a legally-defined subset of returns which are enforced either following a criminal conviction or when it is judged that a person’s removal from the UK is conducive to the public good. Information on those deported is not separately available and therefore the published statistics refer to all enforced returns.
Additionally, the Home Office publishes a high-level overview of the data in the ‘Summary tables’, available from the above link. The ‘contents’ sheet contains an overview of all available data on returns. The latest data relates to the year ending March 2020.
Information on future Home Office statistical release dates can be found in the ‘Research and statistics calendar’ (https://www.gov.uk/search/research-and-statistics?content_store_document_type=upcoming_statistics&organisations%5B%5D=home-office&order=release-date-oldest).