While you are on maternity leave you are regarded as being in employment and therefore employment rights, e.g. annual leave, increments, seniority, continue to build up as if you were not absent from work.

While you are on health and safety leave you are regarded as being in employment and therefore employment rights, e.g. annual leave, increments, seniority, continue to build up as if you were not absent from work.
 
While you are on additional maternity leave you will retain your annual leave entitlements.  This leave is not considered to be a break in service.