Not exactly, Jonathan. That would be more accurate as "In British English, you CAN use 'have' ".

American English would always use the singular verb form 'has' in those cases. In British English, both are possible. We would use 'has' if we are considering the government as a single entity and 'have' if we are considering it as a group of individuals. This is what we call notional agreement. In an international context, I'd recommend using the singular form. This would be seen correct for all English speakers. If you were to use the plural for an American audience, they might assume that you were making a grammatical error.

It depends on whether you consider the entity a single whole, or a collection of parts. The government has its fingers in every pie. The government have their fingers in every pie.

If you are talking about American English use "has." However, in British English you would use "have."

Both of them are singular. So, you should use "has".