Ms Harman's minding the shop while Mr Brown's away
Harriet Harman has sought to end the questions over who is in charge while Gordon Brown is on holiday by saying: "I'm minding the shop this week."
Downing Street had earlier said that Ms Harman was one of "a number of senior ministers in London to deal with the day to day business of government".
The spokesman said "the prime minister remains in charge while on holiday".
But, after her comments, he said "she is the minister who is co-ordinating government business this week".
When Tony Blair used to holiday abroad it became an annual tradition that John Prescott would act as stand-in prime minister during August.
But the prime minister's official spokesman had declined to say that Ms Harman was in charge when he was asked repeatedly about it at Monday morning briefing for lobby journalists.
He said she was one of the senior ministers seeing through the daily business of government - and stressed that Mr Brown was still in charge during his bucket-and-spade English beach holiday.
He did admit that Ms Harman, who appeared on BBC1's Andrew Marr programme on Sunday and GMTV on Monday, "has held meetings in Downing Street this morning".
Later on Monday Ms Harman was asked what her role was by the BBC's Carole Walker, which is when she said she was "minding the shop while the proprietor is on holiday".
After this, No 10 agreed that she was the person co-ordinating the government's work "this week".
Different senior ministers are due to take on the coordination role in the next two weeks - expected to be Chancellor Alistair Darling next week, followed by Justice Secretary Jack Straw.