http://www.harlequin-survey.org/recognition_and_distinction.htm#
Distinguishing the harlequin ladybird from other British species:
• If its less than 5 mm (1/5 inch) in length, it is definitely not a harlequin ladybird.
• If its red with precisely 7 black spots, it is a 7-spot ladybird.
• If it has white or cream spots, it is a striped ladybird, an orange ladybird or a cream-spot ladybird.
• If it is large, burgundy coloured and has 15 black spots, it is an eyed ladybird
• If it has an orange pronotum, and fine hairs all over the elytra, it is a bryony ladybird.
• If it is black with four or six red spots, two of which are right at the front of the outside margin of the elytra, it is a melanic form of the 2-spot ladybird.