The club secretary maintains the membership details which are obtained from you and checked/refreshed yearly when the new season starts.
These are stored in cloud storage (Google) and only visible to Homestead members using the Google login address / password that you provide for access to the HomesteadBC.co.uk "members only" area (thank goodness I sorted out a protected section from the outset).
All members can access a subset of the membership details easily via contact list, can access the source spreadsheet which is the "golden" copy, (or a copy can be exported for you if you request it).
The data held is needed for a number of reasons including but not limited to:
Registration with Badminton England (who still use DOB as a key identifier).
Contact for annual Homestead BC renewals
emailing all about club related matters such as passing on details of tournaments, sorting out renewals, organising meetings.
And most importantly for sharing details between members to ease lift sharing, organising matches and picking up match players.
Whilst you might not directly access the data the secretary gets a steady trickle of requests asking for contact numbers/addresses during the year. It's also why the secretary is keen to keep it up to date.
There is no reason for Homestead BC to divulge any of the maintained data (other than the usual "if compelled to by law" caveat) with people outside of the club and at time of writing the secretary has never done so since becoming secretary in 2007.