For what it is worth my thoughts regarding my original ID were:
I think the thorax is dull. It was a hot sunny day and there is barely a reflection on it.
That would suggest that it is not M. umbellatarum (based on Ball & Morris), their picture (without sunshine) shows a metalic finish to the thorax.
You can even see the reflection of the photographer!
It also suggests that the markings are paler, often creamy white. In real time, my individual was definitely a shade of yellow rather than cream.
As far as habitat is concerned:
Looking at Steven Falk's photographs, I noticed that some were taken in Hampton Wood, Warwick. Which is descibed as "ancient woodland and meadow". I think that the M. compositarum / labiatarum is found in/near conifer forests but in the lowlands it appears to have a different habitat.
Yours G