For many small businesses the business vehicle is the largest asset. So you want to own and use it in the business in the most tax-efficient manner. 

There are several options. The vehicle could be owned by the company/sole trader with the expenses of the vehicle being borne by the business and the purchase cost being met by the company.

Or the director/sole trader can use his own vehicle and claim Mileage Allowance for all business use of the vehicle. 

Which is the most tax efficient option depends on : 

1) how much mileage you will do and

2) the market price of the car.

 If you will be doing a lot of business mileage with the vehicle then it's normally best to keep the car in private hands.  But if your business mileage will be low, and the price of the car is high, it may be best for the vehicle to be held by the company.

PRIVATE USE ------

 
But if the company buys the car and you use the vehicle for private use, you may become liable for income (personal) tax as HMRC view you as having use of a company car.  Tax can be quite high for employee/company directors using company cars. And the company would also be liable to pay National Insurance for providing a company car. 
 
THE BENEFITS OF A COMPANY VAN -  THE ANNUAL INVESTMENT ALLOWANCE.

Company cars normally incur a tax charge on the employee or director as a 'benefit in kind', which can run into thousands of pounds, but vans are exempt from this, as long as you only use it for work purposes and 'insignificant private use' . This means very rarely use it for private use, or only in emergencies.   

The full initial outlay on the van can also be claimed as a Capital Allowance, which means that your taxable profit figure will be reduced by this amount.   For example if you make profits of £20,000 in 2015 but spend £12,000 on a new van in that year, then your taxable profit figure will become £8,000..