Van benefit from 2005/06: reduction because van unavailable
Section 156 ITEPA 2003
When the van is unavailable for any part of the tax year, the chargeable benefit is reduced in proportion to the number of days in that year for which it was unavailable.
In calculating the reduction for unavailability, the van benefit charge is reduced by the proportion of the number of days for which the van was unavailable to the number of days in the tax year.
There is an example at EIM22872.