In between sizes? Size up for more comfort, size down for more compression. 
Leggings
Size XS S M L XL
UK 4-6 6-8 8-10 10-12 12-14
EU 34 36 38 40 42
ITA 38 40 42 44 46
Tops

Size XS S M L XL
Cup size A/B A/B/C A/B/C C/D/E D/E/F/+
UK 2-4 4-6 6-8 8-10 10-12
EU 32 34 36 38 40
ITA 36 38 40 42 44