help in identification

[msv]

I live in UK
I recently saw a butterfly in my garden and would like to know what it was.I
have looked in some books but cannot find it and wondered if anyone can
help.

It was on a flower and its wings were up so i could see the underside.
It was a pale primrose yellow with a circular-ish ( lime ?) green spot near
its wing tip.

When it flew off, it looked as though the top side of its wings had a lot
more green on them.
As I was in the house when i saw it i couldnt get a closer look.
any help would be nice

thanks in advance

mark v

mark at vygus.freeserve.co.uk