Hebrew Character .
(Orthosia gothica)

A close-up of a really common moth.

Information:
Instantly recognisable, despite its colour variability, by the dark mark in the shape of the Hebrew character "Nun" (which, in Hebrew. means 'miracle'). Alternatively you might see the mark as a stylised representation of a horses saddle - either way, it is very distinctive and there are no other moths, apart from the related Setaceous Hebrew Character moth (where the mark is more like a stylised chevron).
They have fore-wing length of 15-17mm and fly March-May when they can be seen anywhere in Britain.