Of course, all the usual caveats apply. This could well be a rogue, and - even if it's not - the Lib Dem support could, theoretically, plummet once the spotlight stops shining on Nick Clegg. But, even so, this remains devastating for Brown, and can only fuel the raging debate about his future. Coupled with the finding this morning that Brown is the party leader most damaged by the expenses scandal, the option of ditching him will be more and more tempting for Labour MPs. This is going to be a fascinating, and potentially bloody, few weeks in politics.
P.S. The ICM poll also has Euro voting intention figures, which make for more grim reading for Labour. Here they are:
Conservatives: 29 percent (-1)