The London mayoral race turned nasty today after the Conservatives were accused of a launching a "coded racist" attack against Labour's Sadiq Khan.
Leaflets sent by Zac Goldsmith's campaign accuse Khan of being a "divisive and radical" politician. Khan's team believe this is a "dog-whistle" to those uncomfortable with the prospect of a Muslim mayor.
"There's nothing about Sadiq that you could describe as 'divisive' or 'radical' so it's pretty obvious why they've used those words," a Khan campaign source told Politics.co.uk.
"We hoped Goldsmith meant it when he said that he wanted a clean campaign - but sadly it appears he's reverted to type."
The row came as the Tories launched a new campaign blog titled Sadiqwatch.com, which seeks to portray Khan as an untrustworthy flip-flopper.
The blog focuses in particular on Khan's newfound opposition to Heathrow expansion, since running to become Labour's candidate. In a parliamentary debate last week, Goldsmith said Khan's opposition to expansion was "as authentic as Donald Trump's hair". The blog also highlights his recent deliberate distancing from Labour leader Jeremy Corbyn, despite previously highlighting associations with his campaign in order to win the mayoral selection.
The Tories today also launched a new campaign attack video titled "who is Sadiq Khan?" At the time of writing, numerous racist comments had been left under the Conservatives' Facebook post highlighting the video.
Khan's camp believe the Tories have launched their attacks on the Labour candidate earlier than expected due to polling last week showing Khan edging ahead in the race.
The poll found Khan six points ahead of his Tory rival. However, the Labour candidate's support was largely made up of younger voters, while Goldsmith retains a commanding lead with older voting groups which have historically been more likely to get to the ballot box.
Labour have so far appeared reluctant to directly attack Goldsmith, either for his background or his political views. However there are signs that could be about to change.
A Khan source told Politics.co.uk that Goldsmith's former editorship of the Ecologist could come under scrutiny.
"If Goldsmith wants to attack Sadiq's record, we'll point out the flaws in his," a Khan camp source said.
"Although in reality his record only consists of five years in parliament voting with David Cameron. And he didn't do anything of note before politics - unless you count his strange opinions aired in the magazine owned by his uncle."