Who is going to guess this one?

[JohnR]

There is no prize for the winner beyond the usual derision found on this forum. For once I know the answer

[Padfield]

I go for green hairstreak... Nice bottom!

Guy

[David M]

That looks like broom rather than gorse.

[JohnR]

Rats .... right for the butterfly. I fear it says something about lepidopterists who can identify butterflies by their bums; I can't identify them when they are prostrate in front of me.
The plant was in fact Bird's Foot trefoil with a shoot of probably Bedstraw, just to confuse.

[David M]

I'm sure Guy could identify a butterfly merely by its left middle leg!

[Padfield]

Hey, the winner was promised derision!

I too thought it was some kind of broom it was on, but yes - now I can see it is BFT and a bedstraw. It was the tail flaps that gave the species away, though.

Identifying butterflies by their shadows can be challenging and fun too!!

Guy