Harriet Harman will become the first woman to run Britain since Margaret Thatcher when she assumes day-to-day control while Gordon Brown is on holiday.

The deputy leader of the Labour Party, who was conspicuously denied the title of deputy prime minister when elected, takes over the levers of power on Monday for the first of Mr Brown’s three weeks away in Suffolk and Scotland. In a sign, perhaps, of things to come, Ms Harman has already caused consternation inside Downing Street. She has produced a list of demands including supplementary late-night briefings on the next day’s headlines, prompting Jeremy Heywood, Permanent Secretary at No 10, to tell staff: “I know guys, please do not shoot the messenger.”

Downing Street had given the impression that only Alistair Darling, the Chancellor, and Jack Straw, the Justice Secretary, would deputise for Mr Brown, leaving Ms Harman’s role shrouded in secrecy. Aides to Ms Harman said last night that they had been surprised that her name had not been mentioned at the time. Yesterday afternoon the Prime Minister had still not agreed how her role would be “briefed” to the media.

The decision to put her in operational control is a significant about-turn. On the day that she emerged as the victor of the deputy leadership contest, Mr Brown’s aides briefed the media that Ms Harman, a veteran women’s rights campaigner, would not stand in for him at Prime Minister’s Questions. They also said that she was not expected to follow John Prescott’s lead by taking charge when Mr Brown went on holiday.

Since then Ms Harman has made two appearances at Prime Minister’s Questions while Mr Brown was away, and she has performed better than many Labour MPs expected, leaving William Hague, the Conservative deputy leader, speechless.

In preparation for her new duties, Ms Harman stunned No 10 staff by producing a list of demands that go well beyond the normal arrangements laid on for the Prime Minister. It appears that several were initially rejected and became the subject of “some discussion” with Mr Brown’s aides before a plan was agreed.

Ms Harman is insisting that she is telephoned each night about 10.30pm by the duty press officer at No 10, starting on Sunday, to give her a summary of the next day’s newspapers and to discuss urgent issues. She wants her private secretary and special advisers to be included in a 7.30am conference call, followed by a daily meeting at 9am around the Cabinet table.

There are signs, however, that she will be on a tight leash during her brief period as queen bee. Downing Street has made plans for just one public event in No 10 during next week, probably to mark the anniversary of the national minimum wage.

Ms Harman has had a prickly relationship with those inside No 10 and other senior Cabinet allies of the Prime Minister. She has told friends that the Prime Minister does not always make enough time for her, and Mr Brown’s allies rarely cite her as a significant force in government.

Ms Harman was blamed in some quarters for Labour’s poor performance at the Henley by-election after using polling day to launch her Equalities Bill, which some believed would alienate white working-class men. There has also been controversy over the role of her husband, the trade union official Jack Dromey, who was Labour Party treasurer during the cash-for-peerages scandal. He was reelected to the role yesterday.

As Constitutional Affairs Minister, Ms Harman had to relinquish any role in House of Lords reform and electoral administration to avoid any conflict of interest after her husband said that he was “kept in the dark” over loans to Labour by millionaires who were later recommended for peerages.

The Prime Minister’s spokesman played down Ms Harman’s new role last night, insisting that she was not running the country. “The Prime Minister is the Prime Minister and remains in charge whether he is on holiday or not,” he said. “There will always be a senior Cabinet figure around to deal with what needs to be dealt with, but he will be kept closely informed.”

Last year Downing Street said that the Prime Minister would still be in charge of the Government while on holiday, because he was staying in Britain. A source said: “He is making sure that he has got a working office at the cottage just in case.” No 10 sources emphasised that the deputising role was much smaller than for Mr Prescott, who moved in to Downing Street when Tony Blair was away.

Mr Prescott once described what the role entailed. He said: “What [being] in charge means is basically you just watch for what’s going on, coordinate activities, and in some cases when I’ve been on the summer watch have had to coordinate activities about Indonesian earthquakes, there’s been floods in the UK, tsunami, all those things require Britain to make a contribution. So I use the Cabinet committee structure to bring everybody together to achieve.”

A firm female hand on the tiller

What Harriet wants

— The No 10 press office will phone her at around 10.30 each night with an initial resumé of newspaper first editions for an early alert to problems

— Both her private secretary and special advisers would be allowed to join in the daily 7.30 morning conference call. She wants the No 10 official chairing the call to speak to her afterwards

— A daily meeeting in the Cabinet room at 9am throughout next week to take her through scheduled business, largely focusing on the events “grid”

— Full access to the government grid from tonight

— One publicity event in No 10 during the week

Harriet Ruth Harman

— Born in London, July 30, 1950

— Educated St Paul’s Girls’ School, York University

— Legal officer to National Council for Civil Liberties (now Liberty) and a QC from 2001

— Elected MP for Peckham in 1982

— Sacked as Social Security Secretary in the first Blair Cabinet in 1998 after feuding and rows over cuts to lone-parent benefits. Appointed Solicitor-General in 2001 and Justice Minister after the 2005 election

— Beat five rivals to be elected deputy leader

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads