In what follows, I am referring only to BrE.
Many 'group words' can be followed by a singular or plural verb form, depending on whether the speaker is thinking of one group or more than one person in a group; so:
The government has decided to do away with the Council Tax. or:
The government have decided to do away with the Council Tax.
However, the word couple is always followed by a plural verb form:
"A couple are trying to reach a mutual agreement."
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