Possibly going into autumn mode early though not necessarily. If yours is one of the Japanese acers they need semi shade, a wind free location, acidic soil or ericaceous compost and to be kept watered. Ours are so well established they can cope with a fair amount of wind but a young tree will end up with burnt leaves. That, however, does not explain all the leaves dropping this early. Are you near the coast and could they be getting salt sprayed?

They're 'autumning early' because we are experiencing seasons that ARE arriving earlier, therefore, you are approaching autumn - as are we down south.
The autumn leaves are falling already and the temperatures etc are indicating the change of the season.

The tradescantia looks dry, which could be due to wind or it being in a dryer area of the garden.
The acer losing leaves indicates the same.

Louise Startinggardening posted a separate Q with the photo of the Acer - typical wind damage.

Thank you to both of you. There has been no lack of water in our garden recently and both the acer and the tradescantia are in damp parts of the garden. Both are also in fairly sheltered positions but it could still be wind damage on the acer. I will try feeding it with ericaceous compost. We are not near the sea so it isn't that.

Thanks again SG

SG check what your soil Ph is but I a m99% certain this is wind damage.