This is a Yellow-barred Brindle (Acasis viretata), which I found sitting on (rather than in) my moth trap this morning. I’ve not been running the trap much yet this year: many nights have just been too cold, and on the warmer nights when I have run it, it has pulled in very few moths. Hopefully this should start to change soon, and I can add more moth-related posts.
Yellow-barred Brindle is quite a widespread moth, occurring in woodlands, gardens, and areas with hedgerows, but in my experience only tends to turn up at moth traps in low numbers; I’ve only ever trapped single individuals here. In the south of England it is bivoltine, i.e. there are two generations per year: adults emerge in May to June, and then again in September to October. Unlike some moths, it’s not particularly choosy over its larval foodplant: many common shrub species are suitable.
It’s a member of the Geometridae, the second most species-rich family of larger moths in Britain. Almost all moths in this family hold their wings flat at rest, and many of them hold them back in the distinctive upside-down heart shape which this Yellow-barred Brindle is resting in. Some moths in other family have simiar resting positions, but you’ll be correct 9 times out of 10 if you narrow your search to the Geometridae when faced with an unidentified moth that looks like this. There are relatively few moths that are bright green in colour like Yellow-barred Brindle, so that helps the identification process enormously. Note though that the green colour is at its most intense in fresh specimens and fades to yellow quite quickly.
There are two excellent websites which contain large collections of photos of British moths: UKMoths and UK Lepidoptera: see the Web resources page for details.