without a picture it is difficult to say. It could be mealy bug that is an insect that has a fluffy white water repellant layer. or it could be a lichen that is colonising the plant. thats a sign of good air quality. or it could be a fungal infection. Can you take a picture and edit your question with it?

Also could be woolly aphid or scale infestation.

Thanks for the replies - I'm not too good at the technology and decided to take action before my daughter came back from holiday to help me with a photograph. 'fluffy white waterproof layer' fitted the bill and I've used tepid soapy water to good effect to remove it. I've also used a broad spectrum bug spray. Hope this all works since the tree was a present (fairly expensive I imagine because it is a good size).