Support for the Greens shot up by four points taking it to nine per cent, coming a day after a separate weekly poll by Lord Ashcroft revealed a three point jump to 11 per cent.
Other small parties were also buoyed - most importantly the Scottish National party, with support rising by one point to seven per cent.
"The parties we used to relegate to the margins with the term "others" are now moving centre stage," said Martin Boon of ICM. "The combined forces of all those outside the old LibLabCon tripoly has never been stronger during three decades of Guardian/ICM polling."
Labour was unchanged at 33 per cent, the Tories were up 2 points to 30 per cent while UKIP and the Liberal Democrats both shed 3 points to 11 per cent.