Hi David. I like the head-on, eye-level shooting angle and the butterfly is posing nicely with its proboscis in the flower. Very good sharpness where you most need it. This is a strong image, as presented, and a few tweaks might make it even better. You might consider toning down the bright stem in the upper right of the frame and you might also remove the bit of leaf in the LLC. As the butterfly is facing slightly to our right, you might add a little more room on that side of the frame - if you have it - or you could crop a bit off the left. This is well done!
My thoughts ran along those of Steve's before I read any comments. Minor tweaks, but will put a bit of polish on a strong image. I particularly like the balance of flash and natural light here.
Thanks everybody for the feedback, I will certainly carry out the suggested tweeks before printing for club competition. You may well be correct with your ID Jonathan, butterfly ID is not one of my strong suites.