The Liberal Democrats are "wobbling jellies of indecision", Boris Johnson has said, as coalition infighting in the Eastleigh by-election goes into overdrive.
The London mayor fired one of his strongest salvos yet against the Conservatives' coalition partners on the way down to Hampshire from the capital, in a move only likely to send coalition relations further into the mire.
Johnson is spending the day helping Tory candidate Maria Hutchings on the campaign trail in Eastleigh, where she is hoping to oust the Lib Dems after the resignation of former energy secretary Chris Huhne.
"The Lib Dems are wobbling jellies of indecision and vacillation, especially Clegg," the mayor said.
"His single-most [significant] contribution to British politics has been to make a U-turn on tuition fees, then to make a song about it.
"There are lots of areas where the Lib Dems are pitifully weak. It's our constitutional duty to kick the Lib Dems in the... Do they have any?"
Eastleigh may not be one of the areas where the Lib Dems are struggling, however, with the party doing all it can to cling on to a seat Tory backbenchers are desperate to take.
The Lib Dem campaign received a blow after it emerged two of the party's councillors were switching to back Ukip.
But bookmaker William Hill still has the Lib Dems' Mike Thornton as the 1/3 favourite to win the by-election, which takes place on February 28th.
The Conservatives are priced at 3/1, with Ukip on 16/1 and Labour out at 28/1.