Conservative leader David Cameron is pursuing "lipstick on a pig" tactics - where his image is at odds with his policies, says Labour.
Mr Alexander: Stepped up attacks on David Cameron
Transport Secretary Douglas Alexander stepped up Labour's assault on the Tories as MPs begin their summer break.
He admitted Mr Cameron had won better headlines than Labour in recent weeks but said they were based on "gimmicks".
But a spokeswoman for the Tory leader said: "This is a sure sign that they are rattled."
She added: "Instead of concentrating on issues that matter, they have resorted to taking potshots."
Mr Alexander, a close ally of potential future Labour leader Gordon Brown, said the Conservatives had tried to learn lessons from how Tony Blair had reformed Labour.
But unlike Labour, they had not stripped everything down to basic values and then rebuilt policies, he said.
He said of Mr Cameron: "While he sounds right-on, he acts right wing. The packaging might have changed but the substance hasn't."
The Cabinet minister gave three examples which he claimed showed the gap between marketing and reality for the Tories.
Mr Cameron had failed to deliver on his promise to take Tory MEPs out of the European People's Party in "months, not years", he said.
The Tories now say the change will not happen before 2009.
Mr Cameron says he is changing the Conservative Party
Mr Alexander said Tory calls for English-only votes in Parliament were a return to the party's pre-1997 anti-devolution policies.
And proposals to reform the railway network would also repeat past mistakes by fragmenting the current arrangements, he claimed.
The Conservatives instead say they made a mistake in dividing train from track and want more integration.
Mr Alexander argued: "There is a fundamental, indeed irreconcilable, tension between the policy instincts and beliefs of today's Tories and the marketing strategy they are pursuing.
"Tory values and the policy instincts that flow from them remain the Tories' central problem and are at odds with the brand repositioning they have endeavoured to undertake over the last eight months.
"The renowned political consultant James Carville has a rather more brutal term for the ploy - he calls it the 'Lipstick on a Pig' strategy."
Mr Cameron is currently in Afghanistan, where he is meeting president Hamid Karzai.
He has insisted his party is changing, with new attention given to childcare, the environment and "well being" issues.
But Conservative peer and advertising tycoon Lord Bell told BBC 4's The Worst Job In Politics - Leader Of The Opposition: "The Conservative Party has not moved one inch.
"David Cameron has convinced the public that he is different to their normal expectation of a Tory leader, brilliantly done, well done.
"He has convinced the public that he thinks the Conservative Party should be different. He has not changed the Conservative Party."
But Conservative chairman Francis Maude said Mr Cameron was doing the equivalent of what Margaret Thatcher had done in the 1970s.
"He is shaking the Conservative party out of the past and making it fit for the Britain of today," he said.
"This includes developing a whole range of new ideas to tackle the big challenges of the 21st century."