UK postcodes are broken down/divided into 4 levels: Areas, Districts, Sectors, and Units.

RegEX for filtering can be found in this post: UK Postcode Breakdown RegEX.

For G12 8QH the breakdown is:
Area - G
District - G12
Sector - G12 8
Unit - G12 8QH

Postcode_Breakdown_text

Geographically this breaks down as:
Postcode_Breakdown