Size: 4-6mm
Basic colour: Metallic dark blue, usually with a green or violet tinge.
Pattern colour: None
Number of spots: None
Pronotoum: As basic colour
Leg colour: As basic colour

Size: 4.5-6.5mm
Basic colour: Black and red/orange-red
Pattern colour: Black spots on red/orange-red elytra
Number of spots: 3 on each elytron, sometimes fused into transverse bands.
Spot fusions: Sometimes
Other colour forms: Sometimes
Pronotoum: Black, usually with a variable red/orange-red mark and lateral bands.
Leg colour: Darkened; brownish, sometimes tinged with other colours.

Size: 4.5-8.0mm
Basic colour: Black and red/orange-red
Pattern colour: Black spots on the red/orange-red elytra
Number of spots: Five on each elytron
Pronotoum: Shiny black
Leg colour: Blackish - may be tinged with other colours.

The largest british Cryptocephalus - distinctively patterned but rare with a UK Biodiversity Action Plan (BAP) page here.

Size: 2.4-3.5mm
Basic colour: Black and dark metallic blue
Pattern colour: Head usually with yellow markings on the top. Pronotum black with front and rear angles yellow. Elytra black with faint metallic blue reflection.
Number of spots: None, though note pattern of pronotum.
Pronotoum: Black with front and rear angles yellow.
Leg colour: Yellow to pale brown; sometimes partly dark brown.
Confusion species: Cryptocephalus parvulus

Size: 2.8-4.5mm
Basic colour: Metallic blue or purple.
Pattern colour: None
Number of spots: None
Pronotoum: As basic colour
Leg colour: As basic colour with a dark metallic blue reflection and dark brown tarsi.
Confusion species: Cryptocephalus punctiger