You can say 'the police are arresting / chasing...'
'the police' is part of collective nouns which can be used in the plural. we then consider the people that are part of this group.
I believe you can use a plural with 'the army', 'the labour (force)'.
We quite naturally use a plural verb with the police, yet seem to prefer singular verbs with the army.
If I were asked to bet on the results, I would feel very confident that most English people would naturally say "The police are coming" yet "The army hasn't yet left Baghdad" and "The labour force is near full capacity".
It's one of those strange things that I've thought about for many years, how strange it is that we naturally use different forms for things that are so similar as the police and the army.
The 'police force', however, would be singular every time.
Although I have well understood your use of the words 'army' and 'labour force' would mainly be in the singular, the CED confirms the possible use of a plural for both these words. Here and there. The OED also mentions it for labour force.
I guess it all depends on context and the locutor's intentions as often.
J'ai un peu du mal quand à comprendre si " police were " signifie " les policiers étaient" ou bien " la police était"...
voici la phrase: police were mystified as to why he should have killed himself..."
It depends what the speaker has in mind, whether they (or he/she) view the noun as a single unit or collective noun.
So either: the police is or the police are.
In the cricket they often say: the England team/the Barmy army are... (instead of "is"). I prefer to say the English team is.
But then they always say the Australian team, not the Australia team.
So there's no 100% perfect fit, answer.
Thank you so much Maître Capello for your suggestion and Dazza for your explanation.
It seemed to me that, indeed, when the speaker has in mind the single unit (as would be the case in my example), the singular could be used, but I kept finding only examples of the plural in dictionaries, so I was wondering if I had dreamed up the distinction