Maiden's Blush Moth Cyclophora punctaria

Maiden's Blush moth
The Maiden's Blush moth has a reddish hue and a bold red line. Wingspan: 18-25 mm; UK flight time: May-Aug.
It has a more flecked background and wavy red line than the larger Blood-vein moth, with a black-bordered edge.
 

Blood-vein Moth Timandra comae

Blood Vein moth
Blood Vein moth
The Blood-vein moth has a yellowish background flecked with grey like the Maiden's Blush and also a bold red line. Wingspan: 23-28 mm; UK flight time: May-Sep (2 generations).
Instead of the two rows of black dots it has a lower grey wavy line; the bold red line is straight, forming either a straight line or slight V when the moth is at rest and the lower edge is continuous crimson/pink rather than broken black.
Blood Vein moth
There is also a small Blood-vein moth (not shown) which, despite its name, is a similar size (18-25mm) and flies at the same time but is a little browner.