Question to the Home Office:

To ask the Secretary of State for the Home Department, what estimate her Department has made of the number of visitor visas that have expired and not been used during the period in which they were valid in each of the last 12 months.

The Home Office does not collate the information requested.

Data on the number of visitor visas issued and passenger arrivals to the UK is published on GOV.UK:

https://www.gov.uk/government/publications/immigration-statistics-year-ending-march-2020/how-many-people-come-to-the-uk-each-year-including-visitors#data-tables