Lord Bates claimed he was “thoroughly ashamed for failing to be in place to respond to a question”, then walked straight out of the House of Lords chamber.
As peers became aware of what the International Development minister was announcing, cries of “no” were heard.
The bizarre incident which left colleagues stunned happened after the Tory peer had been listed to respond to a question from Labour’s Baroness Lister of Burtersett.
He failed to appear at the appointed time of 3pm, finally arriving at the despatch box nearly 30 minutes late.
Lord Bates told the chamber: “With the leave of the House, I wonder if you would permit me to offer my sincere apologies to Baroness Lister for my discourtesy for not being in my place to answer her question on a very important matter at the beginning of questions.
“During the five years of which it has been my privilege to answer questions from the despatch box on behalf of the Government, I have always believed we should rise to the highest possible standards of courtesy and respect in responding on behalf of the Government to legitimate questions of the legislature.
“I am thoroughly ashamed at not being in my place. I therefore shall be offering my resignation.”
Lords’ proceedings had started earlier than usual on day two of the marathon second reading debate on the EU (Withdrawal) Bill.
Lord Taylor found himself taking Lord Bates’ place but was clearly caught off guard, leaving some peers looking baffled at his attempts to answer questions.
The dramatic exit left former foreign secretary Lord Hague looking slightly bemused as he prepared to open the afternoon session.
Lord Hague told peers: “I was going to say it was a pleasure to open this debate. I hope my noble friend, who has given 20 years of strong public service, will resume his place on the frontbench.”
A former MP, Lord Bates returned to government in October 2016 after quitting as a Home Office minister earlier that year to take part in a 2,000-mile trek across South America in which he raised £260,000 for charity Unicef.
Last night Downing Street said the peer’s resignation had been refused.
A No 10 spokesman said: “He has received support from across the House and we are pleased that he has decided to continue in his important roles at the Department for International Development and HM Treasury.”