wrote:

Can anyone offer advice, please.

Our village hall (about 20m x 6m but very high roof) has what I thought
an adequate PA setup - a Shure hand-held radio microphone feeding a
decent PA amplifier (Carlsboro) feeding four Wharfedale Linton speakers
which are mounted (two on each wall), about 4m up and 5m apart - where
the eaves meet the walls, angled downwards.

A fundamental problem here is that you're using 'hi-fi' loudspeakers for a PA.

I guess there's no budget to change this ?

Graham