It's become increasingly hard to distinguish whether it's Zac Goldsmith or his predecessor, Boris Johnson, who is running to become the next Conservative mayor of London.

Pictures of the incumbent are sprinkled liberally across Goldsmith's campaign literature and the Richmond MP rarely lets a minute pass without referring to Boris during interviews and campaign appearances.

Is this a campaign leaflet for Zac Goldsmith or Boris Johnson? Difficult to tell. pic.twitter.com/zUCF1v3DNF — Adam Bienkov (@AdamBienkov) January 8, 2016

Given Johnson's continued popularity and high name recognition among Londoners, this is hardly surprising. If Goldsmith is serious about moving into City Hall then hanging onto the coat-tails of the celebrity incumbent is one obvious way of getting there.

But when it comes to Labour, you could be forgiven for believing the party has never had a London mayor before. Despite borrowing a number of his key pledges, Sadiq Khan's leaflets don't mention Ken Livingstone at all. Unlike Goldsmith and Johnson, there have been no joint appearances between Khan and his predecessor since he won the nomination.

One source close to Khan told Politics.co.uk: "There are no plans for a joint appearance" adding that: "Ken is not part of our team".

The feeling appears to be reciprocated. Yesterday, in an Evening Standard comment piece titled "London needs to vote for Jeremy Corbyn’s vision of a better city", Labour's former mayor failed to even mention Khan once.

In fact there seems to have been a considerable cooling in the relationship between the two men since Livingstone first endorsed Khan last May. At the time there was talk among Khan's rivals that Ken's endorsement was only secured thanks to a promise to include Livingstone in his administration. That has never been publicly denied, but the chance of a joint Ken-Khan ticket now looks much more remote.

Since winning the nomination, Khan has pursued a deliberate strategy of distancing himself from the former mayor.

In an interview headlined: "Sadiq Khan - 'Believe me, I won't be another Ken Livingstone," the Labour candidate told the Jewish Chronicle last September that the party had to move away from its "unacceptable anti-Jewish" image, adding: "I want to reassure you I'm not like the last guy".

If that weren't clear enough, Khan also deliberately distanced himself from Jeremy Corbyn, for whom Livingstone has been perhaps the party's biggest public cheerleader.

Well, if Sadiq wins the mayoralty then there's a Tooting by-election for Ken this summer... V/@ShippersUnbound pic.twitter.com/18ooh88JZ0 — Jim Waterson (@jimwaterson) January 24, 2016

In a remarkable interview with the Daily Mail last year, Khan suggested that Corbyn's refusal to sing the national anthem made him unfit to be prime minister. He also said the Labour leader risked reinforcing "the perception at the last election that Labour is anti-Jewish."

Labour sources confirm that Khan's comments were deliberately timed to head off Conservative attacks on him for being "Corbyn's man".

However, while Khan has placed clear blue water between himself and the Labour leader, his campaign also recognises that Corbyn's support is necessary. Unlike in the rest of the country, Corbyn does retain enthusiastic backing from large sections of London Labour members and supporters and the two men have already been pictured on the campaign trail once. While they are unlikely to be joined at the hip, Politics.co.uk understands there are plans for at least one more joint appearance in the coming months.

That's not least because it is in Corbyn's own interest to claim ownership of Khan's success in London. If Labour does badly in Scotland and local elections in May, then victory in London could be the only thing that stands between Corbyn and an attempted coup. It is for this reason that many of Corbyn's critics in London have spoken privately about sitting on their hands over the next few months. A victory for Khan would be a major setback for Corbyn's opponents. Corbyn needs Khan much more than Khan needs Corbyn.

Yet there is no such obvious joint advantage for Khan and Livingstone. Livingstone has been an antagonising presence among Labour MPs over recent months and Khan's campaign are keen on keeping their distance from the former mayor.

Ken and Khan on the campaign trail together in 2010

If the race were closer then things might be different. Whatever his faults, Ken won the London mayoralty twice and came fairly close to unseating Boris in 2012. He also still has huge name recognition. To watch Ken walk through London is to watch a celebrity, with Londoners both young and old stopping him on the street for autographs and chats. Livingstone is without doubt a divisive figure. But for all those who loathe him, he still retains a great deal of affection among many Londoners. If Khan were struggling, then his campaign might have resorted to hanging off of Ken's coat-tails, just as Goldsmith is now hanging off of Boris'.

Yet the recent YouGov poll putting Khan ten points ahead has changed all that. Whereas Labour were contemplating a bitter and closely fought race, they are now working to hold onto the substantial lead they have already secured. They're not quite running a safety first campaign. Khan's team know they face a struggle to win back the sort of working class outer London voters that the party lost to Boris in both 2008 and 2012. Whatever the polls say, Labour needs to reach beyond their comfort zone if they are to see off Goldsmith in May.

That said, Khan's campaign are also not willing to take any unnecessary risks either. And with Ken's long history of putting his foot in it, Khan's team appear to believe that standing beside Livingstone would be the biggest unnecessary risk of all.