With Boris Johnson in the ICU, who's leading the UK?

Less than a year after Boris Johnson became the U.K. Prime Minister in a landslide party leadership victory, one of his former political rivals is now at the helm of the U.K. government as the prime minister battles the novel coronavirus in an intensive care unit in London.

U.K. Foreign Secretary Dominic Raab, Johnson’s effective number two in charge, has been asked to take over for the prime minister while he battles the illness.

However, Raab finds himself in an almost unprecedented position in British political history.

Tune into ABC at 1 p.m. ET and ABC News Live at 4 p.m. ET every weekday for special coverage of the novel coronavirus with the full ABC News team, including the latest news, context and analysis.

Unlike the United States which has legislation in place establishing the presidential line of succession, the U.K. does not have a clear emergency succession plan for its prime minister.

If the prime minister leaves his or her post, their political party elects a new leader who the Queen then confirms.

Before he entered St. Thomas’ Hospital Sunday, Johnson asked Raab to deputize for him "where necessary."

With the prime minister’s condition worsening during a national crisis, some observers have expressed concern about the extent of Raab’s authority.

The 46-year-old lawyer ran against Johnson for Conservative Party leadership in 2019, staking out arguably the most pro-Brexit stance of the field running.

In a move widely seen to placate pro-Brexit voters, Johnson reached out to the ardent Brexiteer in July to serve as foreign secretary and first secretary of state -- a de facto deputy prime minister.

While Raab’s passion surrounding Brexit gained him many admirers, his ability to communicate during a public health crisis has garnered some skepticism.

In his Monday press conference from 10 Downing Street, Raab struggled to answer how Johnson was still in charge of the government from his hospital bed.

The foreign secretary admitted to reporters he hadn’t spoken to the prime minister for two days.

Just hours later, Johnson’s spokesperson announced he had entered the ICU.

As Raab attempts to consolidate control, another power struggle has surfaced in Johnson’s cabinet.

Michael Gove and Rishi Sunak, two of Johnson’s top cabinet secretaries, have vied to be Raab’s successor if he too becomes unable to perform his duties.

On Tuesday, Sunak, who became the U.K.’s top treasury official in February, earned the title of "designated successor" to Raab.

Gove is self-isolating after a member of his family began showing symptoms of COVID-19.

Speaking at a press conference Wednesday, Sunak told reporters that though Johnson remains in the ICU, he is "sitting up in bed" and "engaging positively" with doctors.

As of Wednesday morning, 60,733 people in the U.K. had tested positive for coronavirus, with 7,097 deaths, according to the Department of Health and Social Care.

ABC News' Guy Davies and Ivan Pereira contributed to this report.

What to know about coronavirus:

• How it started and how to protect yourself: coronavirus explained
• What to do if you have symptoms: coronavirus symptoms
• Tracking the spread in the US and Worldwide: coronavirus map