(Bloomberg) -- Prime Minister Rishi Sunak’s UK Conservative Party faces a by-election test after a key ally of his predecessor, Boris Johnson, said she was quitting the House of Commons.

Nadine Dorries — who served as culture secretary in Johnson’s cabinet, said on Twitter on Friday that she was standing down as the representative for Mid Bedfordshire “with immediate effect.” The 66 year-old gave no reason for her departure, beyond saying it’s time someone younger took over. 

Her departure will trigger a special election in Mid Bedfordshire, which is a typically safe Tory seat with a majority of nearly 25,000. Nonetheless, Sunak won’t be complacent, because his Conservatives have trailed the main opposition Labour Party by a double-digit margin in national polling for months, and are also under pressure in their rural heartlands from the Liberal Democrats, England’s third party. 

In a set of local elections in May, the Tories lost more than a thousand councilors, with the UK’s traditional third party, the Liberal Democrats, making large gains in southern England. 

Moreover, the Liberal Democrats have sprung three big victories over the Tories in special elections in recent years, overturning majorities of 24,000 in Tiverton & Honiton in 2022, 23,000 in North Shropshire in 2021 and and 16,000 in Chesham and Amersham, also in 2021.

“This is a rural seat in the heart of the blue wall, we are in it to win it,” the Liberal Democrats said in a statement on Friday, referring to Dorries’s seat.

Dorries had been tipped to be given a seat in the unelected upper chamber, the House of Lords, in Johnson’s honors list, which is expected to be published imminently — a move that would require her to leave the Commons. However, it is not clear whether Dorries will make the list.

--With assistance from Emily Ashton.

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