I need advise about my Salix Integra

There is a lot of info on this site of Salix integra - just type the words into the search box and click the button. Here is another site which can help you http://www.daytonnursery.com/Encyclopedia/Trees_Shrubs/Salix.htm

Salix integra likes moist, heavy soil and an open situation - it also likes being able to spread its roots, and it can't in a container - that might be why its looking pretty unhappy. I'd guess you don't know how long its been in a pot - it may be that it wants to be put in the garden.

Sounds like your tree needs repotting.
Lift it out of the pot (I bet its a solid mass) Use strong jet of water to hose off most of the soil, trim the roots to one third smaller than the pot size.
Repot in "Sophisticat Pink cat litter" available from Tescos and well rotted pine bark.
Remove dead branches, prune tree and above all, keep potting medium damp! After two Months feed regularly throughout the growing season.
Repot tree yearly.
I hope this helps.
Stan.

Well, Stjohntongue, your potting mix is different, I'll say that!

Everyone, for good healthy root growth "Sophisticat Pink cat litter" does the job. This is the site where I got the information, please check it out:
http://www.bonsai4me.com/Basics/Basicscatlitter.htm
It's amazing!

Interesting indeed though Salix need no special treatment. Just replant it and the roots will be fine. The rootstock is probably Salix viminalis anyway.

This is true, Fractal, however potting in the above mix makes future rootpruning easier as the roots won't be all choked up with soil.