Angela Merkel, the leader of Germany's Christian Democratic Union, is expected to appoint Paul Kirchhof, a proponent of flat income tax, to her campaign team today, in a signal of her intention to radically shake up the German economy if her party wins September's election.

The appointment of the former judge and author of a radical tax reform blueprint to campaign on budget and finance issues comes as the CDU, Germany's largest opposition party, seeks to regain control of its gaffe-ridden, electoral campaign by refocusing the debate on economic issues.

Ms Merkel, CDU leader, will unveil a campaigning team of experts and political heavyweights today.

Mr Kirchhof, who is not a career politician, is unlikely to be made minister in a Merkel government. Yet his appointment to the team underlines the CDU's message that it will not shy away from implementing far-reaching and possibly unpopular economic reforms.

The move is not risk-free. Mr Kirchhof's income tax concept – a flat rate of 25 per cent and the abolition of all tax loopholes – goes much further than the CDU's reform proposal and sparked hefty criticism within the party when it was unveiled in 2003.

Ms Merkel slid in opinion polls last week as the German media focused on deprecatory statements by Edmund Stoiber, leader of the CDU's sister party in Bavaria, about east German voters, the last in a string of public-relations setbacks.

On Saturday, Gerhard Schröder, the chancellor, sought to drag the campaign further away from economic issues by criticising Mr Stoiber and appealing to the US not to attack Iran.

"Until now, the campaign has been very apolitical," Ronald Pofalla, a CDU MP and economic policy adviser to Ms Merkel, told the FT, adding that his party would now shine the spotlight on the SPD government's "dismal" track records.

Mr Pofalla conceded that the CDU had failed to explain to voters why it wanted to raise value-added tax by two percentage points, a keystone of its programme. The extra revenue would be used to cut non-wage labour costs, making German workers, now among the most expensive in the world, cheaper.

"The VAT rise has sunk through among voters," he said. "The related fall in non-wage labour costs has not done so yet. We need to make the link clearer."

In its first attempt to recast the electoral debate, the CDU held a press conference in Berlin on Monday highlighting Mr Schröder's broken promise to reduce unemployment in his second term.

The event coincided with the third anniversary of the presentation of labour market reform proposals, which Peter Hartz, then head of personnel at Volkswagen and chairman of a government-appointed group that prepared the reforms, said would halve unemployment within three years.

Instead, Mr Pofalla said, unemployment had risen by 800,000 while the number of full-time jobs in the economy had fallen by 1.4m. Under Mr Schröder, unemployment reached a postwar high of more than 5m.