Misumena vatia

I was about to dead head the Roses this afternoon when I spotted this little spider.   
The common name is a crab spider so called because they catch their prey in the front crab like legs and because they walk sideways like a crab.  The spider is devoid of pigment which makes them look white but they can change colour (this could take a few days) to suit the colour flower they are on.    They sometimes have a red line along their abdomen, which this one has.
Apparently they are quite common in the south of the UK.