The government has said it will cut taxes.
The government have said they will cut taxes.
*The government has said they will cut taxes.This is often said to be a US/UK thing, although you do hear both on both sides of the Atlantic. I noticed a restriction which I'm not sure I've seen discussed before, and that's how it works when you have a demonstrative (or a pseudo-demonstrative, a term I've just made up, for when a word such as this is used in a non-deictic way, as in "So I saw this band, called The Semantic Plurals, last night").
*The government have said it will cut taxes.
I think, and this is true for me though it may not be for everyone, that if you have a singular demonstrative determiner (this rather than plural these), you can't have a plural verb, it has to be singular to match the determiner:
??This band are going to be playing.But even more interestingly, you just can't have a plural demonstrative determiner - it's far worse:
This band is going to be playing.
*These band are going to be playing.So the semantic plurality of a noun can influence number on the verb, but not the determiner - the determiner has to match the grammatical number of the noun. This is presumably because the features percolate upwards and you'd have a clash at DP level if they didn't match.
*These band is going to be playing.