Damage to the bark, probably from the winter. If its dry as it looks underneath, not oozing, it'll probably be fine, looks like its 'scabbed over' so to speak, but keep any eye on it and if there's any sign of oozing, specially amber coloured fluid, take it out.

Thank you Bamboo. No there is no oozing so far. I would hate to lose it because I actually grew it from a cutting. Should I cut more of it back or allow the new growth to mature a bit first. I think i will take cuttings from it just in case it does have to go. I can't understand how that kind of damage happens. I wondered if I had put the mulch too close to the trunk.

Where you live, it's possible it froze last winter - in colder parts of Europe, they erect willow or rush screens around their bays to give them some protection, so they are somewhat sensitive to really cold temperatures. Cuttings are a good idea. As for pruning again, if its growing, is it necessary really?

Thank you for the tip on protecting them. I will do that in future. I will leave it alone for now although it looks a bit lopsided. I will also do the cuttings. Since our neighbours changed there bungalow for an 8.6m high house which is supposed to be one and a half height we now have a frost pocket in this south facing garden. Thank you for the advice. I will let you know how it does.