Clive,
Hire purchase means the van is an asset, you can claim tax relief on the interest charged, as well as depreciation. You can pretty much do what you want with the van, except sell it before the finance is settled. You're liable for all servicing & maintenance costs (that aren't included in the warranty, albeit they are also tax deductable) At the end of the term, it's up to you to dispose of the van, or keep running it for as long as you want.
Contract hire means the van is a liability - you can claim tax relief on the monthly payments. They normally work on a 3+35 month basis (35 monthly payment, 3 monthly payments up front) but this can vary - check with the dealer. Also, they'll normally quote on approx 10k miles p.a. but obviously if your mileage is higher or lower, you should ask for a personalised quote. With contract hire (and also sometimes with hire purchase) you can add the cost of a service plan - which can be setup to include scheduled services, tyres, and any other consumables. Road tax is also included in the cost (normally). At the end of the term, the van goes back to the hire company and you take a new one (the upside being that your van is always under warranty) - if the condition is not congruent with the age & mileage, they can charge you to put it right.
Hope that helps
