Broadly speaking, from the tone of your question, the business can deduct costs that are wholly and exclusively for business purposes. Anything that is not a business expense but is for the director's personal use will attract tax in some way.
As a general rule for small, owner managed companies, it's often less tax efficient to run your car as a company car. Run it yourself and claim 40p a mile back from the company (tax free in your hands, an expense against CT for the company, 40p for the first 10000 miles, 25ppm thereafter).
I had a query re an apartment recently. The apartment was small and would double as the company's office as well as one of the director's residence.
If the director pays the company rent to the value of the BIK, the BIK charge is nil and the director pays less in rent/bills than if he rented the apartment privately. In this case it might be worth renting the apartment through the company.
Both scenarios are ones where you are best served talking to your accountant and getting the actual numbers crunched as each set of numbers will work out differently.