It seems likely that Chloe Smith will, at the tender age of 27, become the new MP for Norwich North this Thursday. If she does, David Cameron — who has thrown everything at winning, including a record number of visits — will declare a famous victory.

But the by-election — the first parliamentary contest after the MPs’ expenses scandal — shows how candidates are being forced to camouflage their Westminster credentials.

Ms Smith prepared to canvass in Thorpe Marriott, a well-heeled estate on the edge of the city. “I expect people will want to talk about the northern distributor road,” she said. Ms Smith is campaigning as a Norfolk woman on determinedly local issues.

She describes herself as a “business consultant” but is vague about what she does for Deloitte. Perhaps this is because she is on secondment to the Conservatives’ implementation unit. Ms Smith, who is registered as an assistant to James Clappison, a Shadow Work and Pensions Minister, is drawing up plans on how the party would govern once in power.

The reason for her reticence is not hard to divine. On the doorstep Lisa Dixon, a mother of two, voiced a familiar sentiment. “The trouble is the trust has gone. When it goes you can’t get it back, can you? I feel guilty. My great-aunt was a suffragette, but I don’t think I am going to vote for any of you. Go on, do your job — why should I vote Tory?” she demanded of an activist from Boston, Lincolnshire, called Andrea. The activist started talking about immigration policy.

Norman Lamb, the North Norfolk Liberal Democrat MP running the party’s campaign, sensed a potential voter. He went through his patter — Labour can’t win; the Tories are favourites and only the Liberal Democrats can provide a challenge; the candidate, April Pond, is an established Norwich figure (she runs a jewellery shop) and not a professional politician.

Mr Lamb said that Ms Pond has momentum. Unfortunately for her she also has a moat. The expenses saga has evolved a new weaponry of political abuse. But a more serious difficulty is posed by the Greens and UKIP.

Labour’s campaign chiefs contend that the party’s vote is holding up but, when challenged, privately admit that the “Gibbo” factor has made it virtually impossible for it to win. The morose shade of Ian Gibson, the maverick left-wing Labour MP who triggered the by-election after being deselected following controversy over his second-home allowance, haunts the whole contest.

Mr Gibson had his candidacy rescinded after revelations that he claimed almost £80,000 in second home expenses on a London flat that he later sold at a reduced price to his daughter. He announced his decision to quit as an MP immediately rather than wait for the general election.

The Conservatives hope that the Gibson factor will depress Labour’s vote, concentrated around a number of estates in the city, and that simply turning out their own supporters in the constituency’s wealthier suburbs will be enough to deliver victory.

The strategy may be simple enough but implementing it is anything but. All Tory MPs have been told to visit at least three times and have to register with the Opposition Chief Whip.

Senior Tories acknowledge the danger of overkill, while others complain about a lack of impetus in a campaign that is formally directed by Theresa May but overseen by both Eric Pickles and Gillian Shepherd.

A Shadow cabinet minister fretted at the contrast with other by-elections. “There was a real buzz about Crewe — that’s not how Norwich feels.”

Its voters, who had this by-election forced on them, are managing to contain their enthusiasm.

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