'Police' is always used in the pluarl. With other collective nouns in BrE, we can use either, though the plural is more common. With 'company', you'll see the plural being used a lot when talking about the activities of a company, but as a singular if it is being sold, where we're thinking about the company as a single thing. When we think of groups of people doing something together in a group, we tend to head for the plural in the UK.
