snp leader nicola sturgeon said the ` direction of travel ' was towards independence , as she set out her demands for her to support ed miliband if labour falls short of a majority .
but david cameron warned of the ` frightening ' prospect of the snp holding labour to ransom and demanding they ditch new roads and hospitals in england , wales and northern ireland .
david cameron has urged people to vote tactically , to keep a labour-snp government out of power .