Boris Johnson has adopted the election plans of Michael Howard, the man who dismissed him from the Tory front bench four years ago, in the hope that it will bring him victory as the mayor of London.

He has chosen to fight a “below-the-radar” campaign concentrated in the streets and suburbs of outer London boroughs, where his chances of maximising the Tory vote are highest.

The plan is a rerun of the general election campaign fought by the Tories in 2005 when Mr Howard poured resources into mobilising swing voters in seats that he stood the most chance of winning. Although the strategy failed to secure the breakthrough sought by Mr Howard, the success of its targeting operation enabled the Conservatives to gain 33 seats, despite increasing their national share of the vote by only 0.6 per cent.

The former Conservative leader had a stormy relationship with Mr Johnson, whom he forced to make a humiliating trip to Liverpool in 2004 to apologise for insulting the city and dismissed later for lying about an extramarital affair.

Nevertheless, Mr Johnson has turned to the architect of Mr Howard’s election campaign: Lynton Crosby, the plain-speaking Australian who helped John Howard, the former Australian Premier, to four election victories. Since arriving in January, Mr Crosby has toughened Mr Johnson’s campaign messages, highlighting gritty policy issues including gang violence, effective policing, safety on public transport and support for rape crisis centres, bringing in a ruthless focus on the concerns of middle-income Londoners.

The plan drawn up by Mr Crosby, known within the Johnson camp as a “Zone 5 and 6 strategy”, focuses on the outlying areas served by London’s public transport network. It is to these areas, such as Hillingdon and Sidcup, that Mr Johnson has been quietly making campaign visits, often travelling to Tube or railway stations to meet suburban commuters rather than knocking on doors.

The grassroots nature of the campaign is reflected in its organisation, with priority being given to a network of supporters in target seats and “captains” being appointed to lead canvassing in each ward. About three quarters of target areas have such teams in place.

Like all candidates in the mayoral election, Mr Johnson is seeking to broaden his appeal well beyond traditional Conservative supporters to suit the voting system, which gives each Londoner two votes, a first and second preference, and emphasises the importance of personalities rather than political affiliation.

Policy papers issued by the Johnson campaign have no reference at all to the word Conservative. They are marked with his slogan “Back Boris” and come with covers in a variety of colours, from familiar Tory blue to imperial purple and pink.

Ken Livingstone, the incumbent Mayor, who opinion polls suggest is trailing Mr Johnson and who unveils his environment manifesto today, has similarly avoided branding himself as the Labour candidate. His website, again making liberal use of imperial purple, simply highlights the name Ken with his slogan “Vote for London”.

Brian Paddick, the candidate for the Liberal Democrats, has a campaign website illustrated in grey and blue, rather than his party’s traditional yellow or orange, and his campaign slogan motto “Serious about London”, although he is pictured with Nick Clegg, the Lib Dem party leader, on its front page.

The use of the supplementary vote system to choose the mayor makes it almost certain that second preferences will prove decisive. If no candidate wins 50 per cent of first preference votes, then all but the top two candidates are eliminated and the second preference votes of defeated candidates are distributed between the final two.

The capital will also elect 25 members of the London Assembly, 14 by the first-past-the-post system in constituencies, with 11 London-wide list members elected using the additional member system.

Nominations for the London elections close on March 28 and the deadline for applications for postal voting on April 16.

Public figures

37 days to go until election for mayor of London, on May 1

£9 billion Mayor of London’s budget

£137,579 Mayor’s salary

5 million London’s electorate

37% turnout in mayoral election 2004

£10,000 deposit to stand for mayor of London; biggest in a British election

Source: London Elects

Betting odds

4/9 fav Boris Johnson (C)

13/8 Ken Livingstone (L)

20/1 Brian Paddick (LD)

100/1 Sian Berry (Green)

Source: Ladbrokes

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