It's a distinctively British phrase that adds a friendly or light-hearted tone to a statement.

British Quirk

Suggests the speaker is insisting on something; often used to reinforce one's point in a discussion.

Assertive Nuance

Can stress the speaker's disagreement or correct someone else in a somewhat polite manner.

Used to strongly agree with someone or confirm that something is absolutely correct.

While it adds emphasis, it also softens a statement, avoiding harsh or serious tones.

Sometimes used in comedy to mock seriousness or to parody formal British expressions.