Victorian Premier Jacinta Allan has ordered her caucus members to get out to the formerly safe seat of Werribee in Melbourne’s west on Saturday, amid grave fears Labor could lose the seat for the first time since 1979 at a byelection.

Pollsters say a loss in Werribee could spell the beginning of the end of the Allan government. Victorian Labor headquarters has thrown record levels of cash at the byelection campaign, including on social media advertising, billboards and leaflets, an MP speaking on condition of anonymity told AFR Weekend.