Hamamelidaceae, otherwise known as Witch-hazel or Winterbloom. There are some pics in my gallery.

http://www.growsonyou.com/photo/slideshow/326783-witch-hazel/member/bathgate

http://www.growsonyou.com/photo/slideshow/326782-witch-hazel/member/bathgate

and Amy's picture

http://www.growsonyou.com/photo/slideshow/327069-hamamelis-ruby-glow/all

Prunus subhirtella (winter flowering cherry)

Some of the taller kinds of flowering quince (Chaenomeles)?

Bathgate - thanks for those pictures but I was thinking of more blossom like flowers.
Steragram - I seem to think that here is a winter flowering cherry like tree but the flowers are smaller and more delicate? I suffer terribly with black fly on my other spring/summer flowering cherry so am a bit reluctant but that wouldn't be a problem in winter/early spring?
Tugbrethill - I had a look and I like the 'pink lady' variety but ideally would like it in a ornamental tree variety, not a shrub.

Whatever you're looking for, I'm sure you can find it. Good luck

I have Amelanchier canadensis in my front garden. Mine is a large shrub but can be purchased as a tree. It will come into flower within the next week or so. The white flowers will be followed by black fruits (non poisonous) which will be readily eaten by the pigeons and blackbirds. The leaves will turn golden in the autumn. Also known as the Snowy Mespilus or Service Berry.

what about one of the Viburnums, some are very early but cant bring names to my mind. Dawn seems to stir memories.

Some of the bigger Chaenomeles can reach small tree stature, but will need frequent pruning to keep from turning into a thicket.

Steragram's suggestion (Prunus Autumnalis) is very pretty and long-flowering . . . also Prunus 'The Bride'.

Yes the cherry does have smaller flowers than the later ones (pale pink)but you can't have everything! It would be surprising if black fly were to be about so early in the year.
The Bride (white and single) is probably prettier but its later too.
Almonds have lovely blossom too but are much fussier about soil and weather conditions.We lived near one for 20 years and only saw it fruit once, though it did blossom every year.

Thank you all for your suggestions. My favourite is amalschier canadiensis so will try and source one locally.

Good choice: ours is in bud right now, so usually pretty white blossom end March / early April for two or three weeks.

So disappointed. Went to (rubbish and overpriced) garden centre where I spotted a 'amalanchier canadiensis' but it was in such bad condition I certainly wouldn't buy it let alone for £50! Oh well, my quest continues....

That's a shame Amsterdam. Maybe have a look at Prunus kojo-no-mai? (in flower now)

Amsterdam, sorry that you cannot find a decent specimen but why not go on to Frank P Matthews Ltd site. It will guide you to nurseries in your area who sell their trees. I have found them to be one of the best suppliers in the country. They also appear on YouTube to give you a insight to their trees.