Confidence: It's likely to be this, but I can't be certain.
Notes: Quite a worn specimen with much wing marking gone, not the best image but the scalloped hindwings and overall shape are right for the species, which can be found in flight at this time of year. I've recorded the species before at the same hazel covered hillside but usually much later in the Spring. E. crepuscularia was formerly used for Small Engrailed and E.bistortata was used for Engrailed but the species are now considered conspecific as- "they cannot be reliably distinguished on wing markings or genitalia." (from notes on page 150 in Waring, Townsend and Lewington 2009)