House of Commons Speaker John Bercow made the change after a Liberal Democrat MP, Tom Brake, asked a question during a session yesterday without his tie on.
He was challenged by Conservative MP, Peter Bone, who asked the Speaker why Brake was being allowed to address the House without the appropriate neck-wear.
"It seems to me that as long as a member arrives in the House in what might be thought to be business-like attire, the question of whether that member is wearing a tie is not absolutely front and centre stage," Bercow said.
It has been long-standing parliamentary convention in the UK that male MPs must wear both a jacket and tie as part of a set of rules governing conduct and courtesy in the Parliament.
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But the Speaker has discretion about who he can call to speak in the House and Bercow is known for his unconventional ways and efforts to break down a stiff upper lip approach of doing things in Parliament.
"Convention has been that for men, a jacket and tie is expected; for women the equivalent level of formality should be observed," the guidelines issued to MPs reads.
The Erskine May Treatise on the Law, Privileges, Proceedings and Usage of Parliament,a parliamentary practice guide regarded as the last word on parliamentary etiquette, also states that the dress code rules are a custom rather than a rule.
"It remains the custom for gentlemen members to wear jackets and ties, but the Speaker has not enforced the practice in all circumstances," it reads.