Pool vans for my team — how is van benefit different from company car tax?

I run a small business in London and my team increasingly needs to travel between sites, collect stock, and visit customers. I am considering two or three vans that staff would share, rather than giving anyone a dedicated vehicle. How does van benefit tax differ from company car tax, and what makes a van count as a pool van with no benefit charge? What conditions must be met, such as where the vans are kept overnight, who may use them, and whether they can be used for private journeys? How does incidental private use, or taking a van home occasionally, change the position? I also want to understand record-keeping, fuel, insurance, and what happens if one person ends up using a van far more than others. Practical examples would help.