In the House of Commons, an MP who cannot attend a vote can be paired with an opponent, who agrees not to vote either. The arrangement is not a rule of the House. It is an agreement between members.
In July 2018, Jo Swinson, on maternity leave, was paired with Brandon Lewis. Lewis voted anyway in divisions on the Trade Bill. Reports said the Chief Whip, Julian Smith, had asked five Conservative MPs to break their pairs, and Lewis was the only one who did. Lewis and Smith both apologized. Prime Minister Theresa May called it “an honest mistake made by the whips in fast-moving circumstances.” Swinson rejected that explanation.