As a van is classed as Plant & Machinery for tax purposes, there may be a significant tax planning opportunity to acquire the van prior before the end of the tax year, as assuming your accounting period ends on 5th April 2009, you will receive tax relief on the purchase 12 months earlier than delaying the purchase untill after April 2009.
This is because you can now deduct 100% of the first £50,000 spent on plant and machinery under the new Capital allowance Annual Investment Allowance (AIA) introduced in April 2008. This can be claimed whether or not the van is new or second-hand, purchased outright or is financed via loan or hire purchase agreement.
You have mentioned that purchasing the van earlier may require you to raise finance through a loan. As the loan is used to fund the purchase of equipment for your business, the interest paid will allowable when establishing your business profits, and if you are a higher rate tax payer, could provide you with upto 41% tax and national insurance relief on the interest you pay.