I think you need to draw the distinction between a lease/HP and a loan
Under a lease you will never own the asset, merely rent it, any VAT charged will be allowable provided the vehicle is used for a taxable purpose. The advantage here is that you can get a brand new one hassle free at the end of the lease. A tax deduction will be available for the lease rentals paid
Under HP, this is merely a lease then an outright purchase, once your last payment is made, no VAT is charged on the rentals as this is treated under VAT law as an exempt transaction i.e. just a loan.
Again the HP rentals will be deductible for tax purposes.
The problem here is at the end of the HP agreement you own a vehicle maybe 4-5 years old, which you have to go to the bother of getting rid of yourself
Lastly, a loan to acquire, any interest will be deductible for tax purposes and you may claim the VAT back provided its a commercial vehicle and is used for taxable/vatable purpose
using all that its up to you.