We do have a constitution, its just not a written constitution.
Its also the longest running constitution in the modern world, no civil wars/revolutions/changes since the 1660's.
I can't think of another country in the world, thats had a 'same' system in place for anywhere near as long, without having revolutions, civil wars, and generally killing lots of themselves.
If it aint broke, dont fix it.
@Rog,
made me proud to be English.....