After soaking the brown willow another 24 hours, I tried once more to bend it to form the ribs of the rib basket I am making. Once more the willow broke. It seems that it has become too brittle after a year or two in storage.
The trashcan full of brown willow is now outside in readiness for next week's pick-up of garden trash.
I now have some white willow (willow with its bark removed) in soak. I have had better success with using white willow as ribs in the past since it tends to bend without breaking. The reason I chose brown willow for this rib basket was because of the contrast between its colour and the colour of the walnut dyed flat cane. The contrast with the white willow will now suffice.
If all else fails, I will be cutting and stripping more white willow next week. It looks as if it is ready to strip since the first flush of leaves has come.