How well have you been watering it? A new tree needs a lot of water to enable the roots to establish properly.

Sounds like lack of water, have you kept it watered?, It's been quite dry lately, and newly planted trees need a lot of water until they get established, Derek.

Snap, Mg, Derek.

Indeed snap Derek

Derek,
You may be watering in the wrong way, ie if your just watering over the ground above the tree it will depend on what time of the day your doing this ie if its warm or hot day and your water during the day chances are most of the water never gets to the trees roots as it evaporates,

After the plant was left in a good wide bucket to really soak the roots it should have been planted in a wider area than the roots and then after slow acting fertilizer was applied and the area filled with good soil/compost and staked, the plant again should have more water to help settle the roots and then one of two good tips you can do,

(1) get yourself 4x plastic milk bottles and remove the base, take the screw top off and make a hole in the outer area of the hole you've planted the tree in, place the narrow end of the plastic bottle into the soil/comost at an angle so the bottles pointing towards the centre of your tree,
Do this 4 times around the tree and have about 1/4 inch of the bottle above the ground,
you've now got 4x water feeding devices that will get the water down to the roots quick "this method can also be used for applying feed,
All you do is apply your water into each bottle.

(2) if you use the above method and "now" provide a mulch around the base of your tree, this mulch keeps the roots from drying in hot weather and the area moist.

Water the tree of an evening when the ground is less likley to dry in the hot weather, that way the roots are getting watered.
Once the tree has settled after the summer these plastic bottles can be removed "but " for the first year i"d keep the mulch around the base of the tree it really helps during the winter to stop the roots suffering from freezing conditions.
Ive planted many trees and used the above method with very good results.

Sorry Dungy, foxhaven asked the question, I just commented on it, Derek.

Sorry Derekm
I meant it to go to foxhaven.
My mistake.

These drying winds and occasional night frost won't help either, its been a tough time for trees and shrubs this spring

Just a thought, could it be you have betula pendula purpurea?
There was an established birch in my garden when I moved in some years ago now. It wasn't until it started to produce spring green leaves a couple of years ago that I realised it wasn't the common silver birch. (How observation am I? Lol)
Take a look at http://www.ornamental-trees.co.uk/ornamental-trees-c18/betula-pendula-purpurea-tree-p42 It may surprise you :-)