Shrub for space shown in photo
I am looking for a shrub that wil grow quickly to a max height of 3m by 4m
Cornus siberica or a dark purple buddleia might do the trick, unless you want an evergreen then an escallonia might work. I'm sure others will have more suggestions.
North East Somerset - Clay soil over limestone
Pyracantha are mostly evergreen and grow pretty fast. Lovely colourful berries in autumn/winter but they are very thorny...