Hi Jonathan Feacy,
If it was a leasing arrangements where there is no option to purchase the vehicle at the end of the hire period, then any payments under this type of plan would be treated as expenses for renting the vehicle and capital allowances would not be at point.
If, however the contract was a hire purchase or similar contract (where the person makes use of the asset while paying for it in instalments and where title shall or may be transferred on performance of the contract or for a nominal sum), then. you might be entitled to claim capital allowances and you would need to consider this guidance: https://www.gov.uk/hmrc-internal-manuals/capital-allowances-manual/ca23310
CA23310 - Plant and Machinery Allowances (PMA): hire purchase: notional ownership CAA01/S67