How can I find out if an Alpine is in use?

First please check the DVLA website.

A search of club records can be made, this can be done by using the Trace Alpine Form accessible from 'The Club' > 'Sunbeam Alpine Register' link from the main menu. 

Complete as much as possible and click Submit. 

A response will be sent to the email address you give, however due to Data Protection Law only limited data is retained and can be provided to you.