Hi - You can order them online through www.gro.gov.uk/gro/content/certificates/

They are cheaper if you give them the exact refs which you can find on film/fiche of the GRO indexes held in public or genealogical libraries, or online through Ancestry and other paid websites. Also Free BMD: www.freebmd.org.uk/ has now completed many years - with free access, as it says.

Marriages Jun quarter 1869
Surname First name(s) District Vol Page
Evans Elizabeth W. Derby 8b 597
Kermeen William W Derby 8b 597

(I can't be 100% sure of this birth entry, but it has a good chance of being right.)
Births Dec quarter 1870:
Surname First name(s) District Vol Page
Kermeen William W. Derby 8b 455

Let me know how you go.

Sue