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I still think Hibiscus - such as Hibiscus Ardens Shrub, flowers in August' You asked about pruning? Prune in winter or early spring Frequent severe pruning gives fewer but larger flowers hardly any pruning gives more but smaller flowers.
Re its identity though lets see what the others think?

I have never touched it since we moved in and left it because of its shape, i was looking at the Weigela you suggested i think it would look good next to the acer but do you know how big they get as i dont want anything that will dwarf it.

They can get too big to be next to the Acer, mine get about 7ft every year and thats with heavy pruning.
There is a page of Acers on here grown by members which will help you get the right look! Just scroll down and press A then select 'Acer trees'