Liberal Democrat MP John Hemming used parliamentary privilege to name the footballer in the House of Commons on Monday afternoon.
Mr Hemming, who has been campaigning on the issue, said: "With about 75,000 people having named Ryan Giggs on Twitter, it is obviously impracticable to imprison them all."
House of Commons speaker John Bercow took the MP to task over his action, saying: "Let me just say to the honourable gentleman, I know he's already done it, but occasions such as this are occasions for raising the issues of principle involved, not seeking to flout for whatever purpose."
MPs and peers cannot be prosecuted for statements in the chamber of the House of Commons or in the House of Lords, even if they break the law.
Giggs is alleged to have had an affair with former Miss Wales and Big Brother contestant Imogen Thomas, but his lawyers prevented the publication of the story by taking out a court order claiming it infringed his rights to privacy. This prevented not only publication of the story, but also prevented any mention of it in the media.
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