I think this is a first-brood male green veined whiite/Pieris napi butterfly, taking an early lunch at Borthwood Copse on the Isle of Wight last spring. Equipment used was a monopod mounted Canon 400D plus 300L IS lens and 2x converter.
Camera: Canon EOS 400D DIGITAL (Canon)
Focal Length: 600 mm
Exposure: 1/250 sec
Aperture: f 16