After Tuesday's bruising LBC radio debate the London mayoral election appeared to be descending into a nasty needle-match.

That may have been inevitable. The Conservative party generally, and Boris Johnson's team in particular, have too much riding on winning to do anything other than fight brutally to cling to City Hall.

The problem is compounded because the Tory campaign has what Downing Street was reported to believe is an 'underwhelming' campaign based on no real 'retail offer'. In such circumstances pure negative campaigning was the likely route for the Tories.

Pressure to go negative was bound to intensify once it was clear that Ken Livingstone's campaign would offer popular, clear messages that appeal to wide groups of voters. The Fare Deal fares cut is top of that list and is significant in constituencies like mine in Feltham and Heston where a person earning the minimum wage can find themself having to spend up to 14 weeks pay a year travelling to work in zone one.

If anything represents the negative thrust of the Tory campaign it is the extraordinary sight of Boris Johnson's 'NotKenAgain' bus rolling around London. London has never seen anything like it - a totally negative bus tour, thousands of pounds spent on driving around the capital churning out a negative personal message.

But even so, the fall-out from the LBC hustings was all about the personality battle. As Karen Buck has warned, this risks alienating the voters.

Ken Livingstone's quick, dramatic move to raise the tone by shutting down his attack website chickenfeed.org.uk and appealing on his rival to close his own attack site, coupled with an appeal to focus on the issues that Londoners care about, offers a way to pull things back from the brink. It has been well-received, with backing from the Green candidate and very positive coverage.

But so far it has fallen on deaf Tory ears. All day, Boris Johnson's backers on Twitter, have been trying to draw Labour supporters into rows. The Tory campaign has broadly said get lost - issuing a statement that indicates it has no intention of giving Londoners the kind of election campaign they deserve. The Tories' campaign director, who must take equal responsibility with Boris Johnson for the strong negative emphasis of his campaign, tweeted in support of his attack site.

The problem for the Tories is threefold. One, Boris Johnson's ultra-negative campaign now risks feeding the re-toxification of the Tory party, a process underway after the budget, the NHS Bill, the granny tax, the pasty tax and the jerry can fiasco. It looks like the nasty party is back. Two, it equally risks toxifying Boris Johnson's personal brand. Three, and most importantly, the Conservative campaign looks like a campaign that doesn't understand the voters' wish to hear the issues at stake in the election, and understand what the mayoral candidates will do for them.

The Newsnight debate tonight can change the terms of the election. The candidates can have a debate about fares, police, housing, the cost of living - the things the mayor can really change.

Both campaigns say the issue is who will make you better off - "Better Off With Ken vs Better Off With Boris." Let's have that debate tonight. It is what Londoners want, and what Londoners deserve.