Hung parliament
Ben Page of Ipsos said the Tories were as popular as "a cup of cold sick".
The prime minister says the local elections show the UK is heading for a hung parliament.
Study based on YouGov MRP poll suggests just 21,215 voters can decide election if they vote tactically to deny the Tories in 30 seats they are currently expected to win.
Former Labour leader suggests government of national unity could run UK - without Corbyn as PM.
"What I am offering to the public is a Lib Dem government."
The pair disagreed during BBC Two’s Politics Live broadcast over whether the EU referendum result in 2016 or MPs elected to parliament should decide the future of Brexit.
Former PM says snap election is too risky for Tories and new people's vote the way out.
The five things you need to know about politics today