LONDON (Reuters) - British Prime Minister David Cameron faces a public test of his government's slumping popularity after a prominent Conservative legislator said on Monday she was quitting for family reasons and moving to join her husband in New York.
The decision by Member of Parliament (MP) Louise Mensch, an author of popular "chick-lit" romantic fiction who entered parliament at the 2010 national election, will trigger a by-election in her marginal seat in Corby in the English Midlands.
Cameron's centre-right Conservatives, the senior party in the two-year-old coalition government, are trailing in the polls behind a resurgent Labour opposition as the economy struggles to recover from the effects of the global financial crisis.
Labour will hope to regain the constituency after narrowly losing it at the last general election, inflicting a short-term blow on Cameron, although doing little to dent the coalition's 83-seat majority in parliament.
The Conservatives' standing with British voters has declined after a poorly received budget in March that cut earnings tax for the richest and raised levies on the elderly, prompting accusations the coalition was out of touch with ordinary people.
Cameron is under further pressure from rebel legislators in his own party who believe traditional Conservative skepticism towards Europe and state welfare is being constrained by the coalition with the left-leaning Liberal Democrats.
Mensch, 41, who wrote best-sellers such as "Career Girls", "Glamour" and "Desire" under her maiden name Louise Bagshawe, won praise for her close questioning of Rupert and James Murdoch in a parliamentary committee inquiry over phone hacking.
A prolific user of the Twitter messaging service not afraid to pose for glamorous magazine portraits, Mensch said she was resigning as an MP and moving to New York as the "best outcome for my family life".
She previously said it was difficult balancing work as an MP with looking after three small children from her first marriage and having a husband living in New York. She married Peter Mensch, the manager of rock band Metallica, in June last year.
(Editing by Mark Heinrich)