This is a green immigrant leaf weevil. It was very difficult to photograph because it was so small and moving very quickly along the garden wall.
It is a pest really and has potential to cause damage to emerging leaves and blossoms so not really a welcome visitor to the garden but it is quite interesting with really vibrant colouring. As you can see from the second image which is a close crop of the carapace the colouring is actually a series of very fine dotted lines (you probably have to zoom in a bit) each dot like a little green jewel.
It is hard to get a true sense of scale when these are enlarged but if you use the grains of sand in the mortar as a guide you will get some idea of how tiny this thing is.