MICHAEL Martin announced today he was stepping down as Speaker next month as the Westminster expenses scandal claimed its biggest scalp.

In an emergency statement, Mr Martin told a hushed House he would "relinquish" his post on Sunday June 21, so a new Speaker could be elected on June 22.

The statement came just a day after he faced unprecedented challenges to his authority in the chamber and a motion of no confidence in his handling of the expenses row was tabled by Tory Douglas Carswell.

It is the first time a Speaker has effectively been forced from office since Sir John Trevor was found guilty by the House of a "high crime and misdemeanour" for accepting a bribe in 1695.

In a brief statement lasting less than a minute, Mr Martin said the House was at its best when it was united.

"In order that unity can be maintained, I have decided that I will relinquish the office of Speaker on Sunday June 21."

He refused to take questions on his decision and moved onto the next business - Foreign Office questions.

The House was crowded and in sombre mood - with the Prime Minister, Tory leader David Cameron and Liberal Democrat leader Nick Clegg present - as Mr Martin rose to make his third, and shortest, statement on the expenses row in just over a week.

Calling the House to order, Mr Martin said: "Since I came to this House 30 years ago I’ve always felt the House is at its best when it is united.

"In order that unity can be maintained, I have decided that I will relinquish the office of Speaker on Sunday June 21.

"This will allow the House to proceed to elect a new Speaker on Monday June 22.

"That is all I have to say on this matter."

He then called the first question to the Foreign Office.

The statement came less than 24 hours after Mr Martin faced direct calls for him to quit but refused to give any indication if he would step down.

In extraordinary scenes in the Commons yesterday, Mr Martin said he was "profoundly sorry" for the public anger over MPs’ expenses claims and called an urgent meeting of all the party leaders to discuss proposals for reform.

But backbench anger over the Speaker’s handling of the crisis swiftly erupted on the floor of the House as a series of MPs directly challenged his authority in points of order demanding he should set a date to go.