My employer has asked staff to provide details to update personnel records.  These include name, address, job title, qualifications. However they have also asked for names and dates of birth of spouse and children.  I can not see how this is relevant. I understand that they may want an emergency contact / next of kin details or need these details for medical insurance / pension but this would surely be asked for by those organisations. 

Why would my employer need to know my spouse’s date of birth?  Under the data protection act do they not need to ensure that any personal information requested is relevant?