Have you been regularly and well watering? Even if it has been raining newly planted trees need to be watered until they are established. I am also not clear from your question if you have planted the Acer autroperpurea and the Washingtonia in the same planting hole. If you have I trust they are a good distance apart as your Washingtonia is gonig to get rather tall. In the case of the Acer it needs to be planted out of the wind and in semi shade i.e. no direct sunlight in the middle of the day and it requires a neutral to acidic soil to grow.

Your Washingtonia would be best kept in a pot - it is frost tender and is in danger of dying if subjected to temperatures less than 10 deg. C, so at least in a pot you can move it somewhere frost free as winter approaches. It may be that, as we had a chilly night this week even here in London, its been affected by the shock of that, but more likely its not getting enough water at its roots. They do not like to dry out completely, and require fertile soil.

thankyou bamboo for replying