Acers need to be in semi-shade not a conservatory. Put outside somewhere out of the wind and direct sun and keep well watered.

Its fried - either too much heat, direct sun between 12 and 3 on hot days, and/or windy conditions. All of these cause this. This is an outdoor plant, not a conservatory one, as Moongrower says.

Yes scorched nearly to a crisp.

How about stripping the leaves and put plant outside somewhere in your garden.

As per the above, Acers have reserve leaves, so they may re-grow this year, otherwise it should look good next year.

I remember another GoY member kept her acers in the conservatory and couldn't understand why the leaves withered...

Experienced exactly the same sickness with a new Acer 3 months ago ,as all have said, put in shade , out of wind. All the leaves will drop off , but bingo, a month later I have nice new green buds opening into lush green leaves.
Be patient.

Well Ian I trust you do not have sitting in a conservatory!

I have never seen one do well in an indoor situation. Also, in a container, if you miss one watering, that ends the beauty of the leaves! If it were earlier in the year, I would recommend trimming the leaves off so it could grow a new crop, but it is just after the cutoff date for that. I would put it outside in dappled shade, watch the watering on it, keep the soil from freezing this winter, and hope for better things next summer.