On Wednesday, the UK's blue-chip index slightly declined as disappointing quarterly results from the advertising business WPP and the consumer goods maker Reckitt Benckiser overshadowed investor excitement over Rishi Sunak's pledge to guide the nation out of an economic catastrophe.
By 0747 GMT, the midcap FTSE 250 index had increased 0.2% and the FTSE 100 index was down 0.1%.
WPP shares fell 3.6% to the bottom of the FTSE 100 as the company lowered its forecast for operating margin expansion, and Reckitt Benckiser shares fell 3.2% despite a promising sales outlook.
Sunak, who was named as Britain's third prime minister in as many months on Tuesday, will need some time to review the specifics of a fiscal statement that was initially scheduled to be submitted at the end of this month, according to foreign minister James Cleverly.
Sunak said he would try to fix the mess left by his predecessor, restore trust in British politics and tackle a “profound economic crisis”.
Shares of Standard Chartered and Barclays slipped even as both the lenders reported higher quarterly profit.
AstraZeneca Plc jumped 2.2% after the British drugmaker said that its experimental drug Capivasertib met the main goals of a breast cancer study.