Sir Lindsay Hoyle joked there are “too many Keirs” as the youngest MP took his seat in the House of Commons alongside two other newcomers.
The Commons Speaker made the quip after Labour’s Keir Mather swore the oath of allegiance to the King as Parliament returned from its summer recess on Monday.
At 25, Mr Mather is now the youngest MP in the Commons – the Baby of the House – after overturning a 20,137 Conservative majority to win the North Yorkshire seat of Selby and Ainsty for Sir Keir Starmer’s party.
Mr Mather was followed by Conservative Steve Tuckwell, who held the seat of Uxbridge and South Ruislip for the Tories after the dramatic resignation of former prime minister Boris Johnson.
Liberal Democrat Sarah Dyke also took her seat on Monday after winning Somerton and Frome.
She takes over from former Tory MP David Warburton following his resignation after he admitted cocaine use.
The three arrivals come at the start of a busy period in politics, with party conference season weeks away, the King’s Speech and two further electoral battles imminent.
Labour and the Lib Dems are both vying to flip a 24,664-strong majority in the Mid Bedfordshire seat of former Tory culture secretary and Johnson ally Nadine Dorries.
Government chief whip Simon Hart asked for the writ to trigger the by-election to be moved on September 12.
Meanwhile, a fight for the constituency of Rutherglen and Hamilton, prompted by former SNP MP Margaret Ferrier’s Covid-19 rule-breaking, will be closely fought by Labour and the SNP.
The SNP’s Owen Thompson moved the writ on Monday to trigger the contest.
By-elections have to take place between 21 and 27 working days from the issuing of the writ, suggesting the Rutherglen and Hamilton contest could be on October 5 and Mid Bedfordshire in mid-October.
