"Liberal Democrat sums just don't add up," Tony Blair used to say. Julia Goldsworthy's task is to prove him wrong. She is their new "shadow" Chief Secretary to the Treasury - so she will add up the cost of Liberal Democrat election promises and make sure they are all covered by the tax proposals. She is a politician with a future - smart, confident, hard-nosed and she has the facts at her fingertips - or has she? The Independent put her to the test.
"At what level of income does a person start paying 40 per cent tax ?" she was asked. "In the mid thirties," she replied. "That's right isn't it? I will have to refresh that kind of thing in time for the Budget." Well, the exact answer is £32,400 per year - so she was close. Next came a question that stumped Stephen Byers when he was minister for Schools. "What are eight sevens?"
"Forty-two," she answered with confidence. Er, sorry, Julia. Forty-two is the answer to Life, the Universe, and Everything, according to The Hitchhiker's Guide to the Galaxy. You could call it the ultimate Liberal Democrat manifesto. But whatever planet you're on, eight sevens are fifty-six. The colour rose up her neck. "Fifty-six!" she cried. "You're right. Gosh that's terrible!" Here she broke into a defensive laugh as she reflected on what the party's "shadow" Chancellor, Vincent Cable, would have to say. "Maybe Vince will be taking me in for an arithmetic test. The press office is no good at arithmetic either. They got my age wrong!"
Turning serious, she added: "I think the most difficult thing for the economy portfolio is keeping track of how many zeros come in. That's where the mistakes tend to come in."
"How many zeroes in a billion?"- "Nine." She got that one spot on.
Ms Goldsworthy is too brimming with confidence to let inexperience or the occasional slip-up worry her, and for someone of her age - she is 27 - she is not a total novice. She went into politics a year after leaving university, at the end of a 12-month visit to Japan. She was from a non-political family of three sisters - her father was a local government worker, her mother a teacher - but she broadly sympathised with the Liberal Democrats, and was looking for a career to test her research skills, so wrote to Truro's MP, Matthew Taylor, for advice. To her surprise, he hired her. Later she spotted an opening to stand as a candidate in her home town of Falmouth. It was a bitter election, in which a gay researcher employed by the sitting Labour MP, Candy Atherton, was allegedly asked to "dig dirt" on the gay Tory challenger, Ashley Crossley. The nastiness probably helped Ms Goldsworthy to come through the middle.
"I don't think anything that happened did people's views of politics much good," she said.
It has been a rapid rise. She is England's youngest MP, and for two days she was the youngest member of any party's front bench team, until Menzies Campbell announced a second batch of promotions which included Jo Swinson, a 26-year-old Scottish MP. Her fame is due for a boost later in the month, with an appearance on a reality TV show for Channel 4, The Games. But she is now debating whether to pull out as it coincides with the week that Gordon Brown will deliver the Budget. "If The Games can fit around that, I'll take part," she said.
She also needs to keep in mind how George Galloway was made to look ridiculous in the Big Brother house, when the whole point of her new job is to make sure that Liberal Democrat policies are not met with laughter.
The idea of belonging to the kind of party the Liberal Democrats once appeared to be - people in open-toe sandals exuding well-meaning incompetence - does not appeal to her.
Tony Blair had a routine whenever he wanted to ridicule them in the run-up to the last election. He would dip into a folder that was said to contain dozens of expensive Liberal Democrat promises which had not been properly costed. Ms Goldsworthy was centrally involved in costing those promises - when her boss, Mr Taylor, was chief treasury spokesman. She is adamant that the manifesto stood up to independent scrutiny. "It was one of those easy hits that Tony Blair likes to take," she claimed. But, she admitted, the ridicule stuck. That is, as she put it, "an area where we lack credibility".
It was the "credibility" question that made her react with horror when she heard Charles Kennedy say - after owning up to a drink problem - that he was calling a leadership election and intended to stand. She is convinced that would have been "death" for the party. She was in no doubt about who should take his place.
"The Conservative Party's problem was being perceived as a nasty party - that's what Dave 'cuddly' Cameron is trying to overcome - whereas for the Liberal Democrats the issue is gravitas and credibility," she said. "Ming [Campbell] is respected across all political parties as someone of integrity and credibility, and gravitas.
"I want to do whatever I can to bring the Liberal Democrats closer to being a party of government," she added. She is almost sure to do that - but first, a refresher course in basic arithmetic might be in order.
* BORN: 10 Sept 1978
* FAMILY: Single, no children; mother a teacher at St Meriadoc School, Camborne, for 37 years
* EDUCATION: St Meriadoc School, Camborne; scholarship Truro School; BA Hons History Fitzwilliam College, Cambridge; One year at Daiichi School of Economics; Postgraduate Certificate in Economics, Birkbeck
* SPORTS: Rowing for Helford River Pilot Gig Club; Competitor in 2006 TV series of The Games
* CAREER: 2003 Researcher for Matthew Taylor MP; 2004 regeneration officer Carrick District Council; 2005 MP Falmouth and Camborne; spokesperson on health; 2006 shadow Chief Secretary to the Treasury
* OTHER: Chair of all-party rowing group; vice-chair of Group on Qatar.Reuse content