Nick Clegg had a harsh message for David Cameron in his keynote conference speech today, as he tried to prove to Liberal Democrat members he was exerting a major influence on government policy.
The deputy prime minister went off-script half way through the speech to mock rumours around Boris Johnson's desire for the Tory leadership.
After highlighting a supportive article Boris wrote about him in the Telegraph, Clegg added: "At least he's found one party leader he's prepared to endorse in public."
He then went on to tell delegates he would not allow the Tories to drop the top rate of income tax any further this parliament or back George Osborne's spending plans after 2015.
"Let me make one thing clear: now that we have brought the top rate of tax down to 45p – a level, let's not forget, that is still higher than throughout Labour's 13 years in office – there can be no question of reducing it further in this parliament," the Liberal Democrat leader said.
The Treasury later told reporters it was relaxed about the speech and Osborne had no intention of lowering the top rate further.
Clegg also berated the Conservatives for failing to commit to green issues in government, and mocked Cameron's own PR initiatives on the environment early in his leadership.
"Let the Conservatives be in no doubt -we will hold them to their promises on the environment," he said.
"Of course, there was a time when it looked like they got it. It seems a long time ago now."
Clegg announced former leader Paddy Ashdown would chair the party 2015 general election campaign, triggering perhaps the biggest cheer of the afternoon.
He also criticised those in the party who had spent much of the conference speculating about a possible deal with Labour in the event of another hung parliament.
"There’s been a lot of discussion on the fringe of this conference about our party's next steps; about our relationship with the other parties; and about what we should do in the event of another hung parliament," he said.
"I have to tell you, it is all based on a false, and deeply illiberal, assumption: that it is we, rather than the people, who get to decide. In a democracy, politicians take their orders from the voters."
In a combative speech which seems light years away from his tuition fees apology, the deputy prime minister also told members there was no hope of them becoming a protest party again.
"The choice between the party we were and the party we are becoming is a false one," he said.
"The past is gone and it isn't coming back.
"If voters want a party of opposition – a 'stop the world I want to get off' party – they've got plenty of options, but we are not one of them."
He added: "There's a better, more meaningful future waiting for us. Not as the third party, but as one of three parties of government."
The tough speech also saw Clegg tell the audience the party has proved its "mettle" - despite defeats on House of Lords reform and AV - by sticking to the coalition agreement and hammering down the deficit.
But in a week in which Clegg has tacked significantly to the left with demands for a wealth tax – probably in the form of a levy on mansions – he did offer party members some redistributive pledges as well.
The speech saw Clegg unveil a new 'catch up premium' of £500 for every child who leaves primary school below the expected level in English or maths.
"Let me reassure you: we will do whatever it takes to make sure your child is not left behind," he said.
"A place in a summer school; catch-up classes; one-to-one tuition; we are providing the help they need."
The initiative is designed to alleviate Lib Dem jitters over Michael Gove's changes to GCSEs, which will see a more demanding Baccalaureate exam introduced to combat grade inflation.
The deputy prime minister, who prevented education secretary Michael Gove from implementing a return to O-Levels, put his reputation further on the line by joint-announcing the new scheme.
Today he promised "every well taught child" will be able to pass the exams.
"Yes, we're raising the bar, but we're ensuring every child can clear it too," he said,
The speech came at the end of a week which saw the Lib Dem leader largely dispel rumours of a leadership challenge, despite disastrous poll ratings.
At the conference centre, most Lib Dem members were uninterested in having a debate about the leadership, although Vince Cable's speech seemed to strongly imply that he was the right man to lead the party if it needed to form a deal with Labour.