If the car is purchased by the company for the director's personal use, no tax deduction can be claimed. Please see HMRC's Capital Allowances Manual, CA0006 in particular which states as follows:
Depreciation of fixed assets charged in the accounts is not allowed as a deduction in computing taxable profits. Capital allowances may be given instead. Plant and machinery allowances (PMAs) give relief at prescribed rates for the depreciation of fixed assets that are plant or machinery.
In order to qualify for PMAs, a person must:
- be carrying on a qualifying activity CA20010, and
- incur qualifying expenditure (CAA01/S11).
Qualifying expenditure is capital expenditure on the provision of plant or machinery CA21000 wholly or partly for the purposes of the qualifying activity (CA20010). Normally the person must own the asset as a result of incurring the expenditure.