Nick Clegg mounted a strong attack on his coalition colleagues today, as the Eastleigh by-election campaign began in earnest.
The deputy prime minister used a speech on tax and fairness to highlight the "open secret" of the difference between his party's approach to the issue and that of his partners in government.
Conservative bitterness at the Lib Dems is expected to be channelled into a hard-fought campaign in Eastleigh, where a by-election is taking place on February 28th after Chris Huhne's resignation earlier this week.
Despite the former Cabinet minister's disgrace and a majority of just 3,864 the local Lib Dems are expected to mount a strong defence, having a reputation for solid by-election performances and all 36 wards in the parliamentary constituency.
Clegg explained why his party has called for a mansion tax or a new higher council tax bend to make the rich contribute more to the coalition's deficit reduction drive.
"Both of these options are based on a very simple principle: That we should ask a small number of very wealthy individuals to make a reasonable contribution, in order to provide desperately needed help for millions of ordinary people," he said.
"Nothing could do more to demonstrate a commitment to greater fairness in our tax system. It's an open secret that our Conservative partners do not share our views on this."
The Lib Dems will base their three-week campaign around arguments about tax, with literature pointing out that 61,100 people in Eastleigh received a £600 tax cut in April and 3,880 people have been taken out of income tax altogether.
"This is Nick firing the starting pistol on the Eastleigh by-election," a source close to the deputy prime minister said.
"It's a speech that sets out the distinctive approach of the Liberal Democrats in the coalition government when it comes to tax.
"This is going to be a very keenly contested by-election and Nick is eager to remind the voters of Eastleigh, as well as the rest of the country, that the Liberal Democrats are cutting taxes for those on low and middle incomes."
Huhne won a three-point swing from the Tories to the Lib Dems in 2010, despite intense pressure on his marginal seat from the Conservative challenger.
While media attention will focus on the sudden outbreak of hostility, local politics has seen open warfare between the Tories and Lib Dems for months.
Conservatives have attacked the Lib Dem-dominated council of spending on "risky ventures" and "vainglorious projects" including a new hotel at the Rose Bowl cricket ground. It has also criticised a decision to move the council's offices to the town centre, at a cost of £10 million.
Labour is also hoping to improve its standing in the seat as its previously squeezed vote becomes freed up by the coalition.
Shadow chief secretary to the Treasury Rachel Reeves commented: "This is a laughable speech from an increasingly desperate Nick Clegg. The Liberal Democrats will be judged on what they do not what they say, and their record is the Tory record - one of economic failure."
Eastleigh is no stranger to odd by-elections. In 1994 constituents had to vote once again after their MP Stephen Milligan, a Conservative, was found dead from auto-erotic asphyxiation. The seat has been Lib Dem ever since.