There are two situations possible here:
1. Part of the plant and machinery is not used. In this case, depreciation can be claimed as it forms part of a block of assets and this block is entitled to depreciation.
2. Whole of the plant and machinery is not used during the year. In this case, it can be tricky as obviously no business activity has been carried out during the year and hence the depreciation claim can be negatived as it was not " used " during the year. I doubt if "passive usage" concept can be applied in this case as there was no business activity at all.