the scottish first minister she would form an anti-tory alliance with labour and other smaller parties regardless of how many mps david cameron wins on may 7 .
the snp could win as many as 50 mps in scotland - allowing mr miliband to become prime minister even if he falls far short of a majority .
her comments came as labour slipped four points behind the tories in the latest polls - with david cameron 's tories moving to 36 per cent .