By purchasing equipment for your business before the end of your accounting period, you can receive tax relief in the form of capital allowances. The amount of tax relief you receive depends on whether you are a higher rate tax payer (currently 40%), or a basic rate taxpayer (20%). You will also receive National Insurance Class 4 relief of either 1% or 8% depending on the level of profits for the year.
Under current rules, the majority of small businesses are able to claim a 100% Annual Investment Allowance (AIA) on the first £100,000 of expenditure on most types of plant and machinery (except cars) in the 2010/11 tax year. Any expenditure exceeding this level will receive 20% writing down allowance (WDA).
Vans qualify for the AIA allowance, and therefore assuming you do not have any private use of these items, the full cost of the new van and other items will be offset against your self employed profits in the year.
You should also be aware the new government recently proposed a reduction in capital allowances rates. From April 2012, the maximum amount of AIA will reduce to £25,000, and the standard writing down allowance will also be reduced to 18%.