Conservative Party chairman Baroness Warsi has condemned the violence during a demonstration against student tuition fees, saying it had "helped nobody".
She was inside the party's head office in London when its ground floor was occupied by protesters and some of its windows were smashed.
She said the violence of a small minority had "spoilt" what had been a "legitimate" protest.
The coalition had to take "difficult decisions" in tough times, she added.
'Spoilt for others'
Baroness Warsi said Conservative Party staff in 30 Millbank, located not far from Parliament, were fine and many had continued working while their building came under attack.
The scenes unfolded during what had started out as a peaceful demonstration by thousands of students protesting against proposals to nearly treble university tuition fees in England from 2012.
"Sadly a few, in that protest, spoilt it for other students who had come out to legitimately voice their concerns," Baroness Warsi told the BBC News Channel. "That was the sad part of today.
"Of course it is right that government make policies and people have a right to protest when they disagree. But when that protest turns ugly and resorts to violence that helps nobody and certainly does not take the debate forward."
The straitened financial climate meant ministers had to make tough decisions to ensure universities were financially strong and could continue to compete internationally, she said.
But she insisted the government had sought to make the student finance package as fair as possible, including raising the level at which students begin to repay money to £21,000.
"We have sought to protect the most vulnerable and made sure tuition fees are not paid upfront and therefore it does not deter people from going to university."
Lib Dems under fire
Leading politicians, including Mayor of London Boris Johnson and Lib Dem MP Tim Farron, have condemned the violence.
The National Union of Students, which organised the demonstration, has followed suit - saying the disturbances were the work of a "small minority".
Earlier on Wednesday, Deputy Prime Minister Nick Clegg was repeatedly criticised by Labour MPs in the Commons over his party's U-turn on tuition fees.
The party's MPs all signed a pledge before the election not to raise the cap on fees but Lib Dem ministers in the government argue the change was forced upon them by the scale of the deficit and the financial challenges facing universities.
Standing in for David Cameron at prime minister's questions, Mr Clegg was bombarded with questions by Labour MPs about plans to raise the annual fees cap to £9,000.
Deputy Labour leader Harriet Harman said he had been "led astray" by Tories who wanted to "shove the cost" of degrees onto students but Mr Clegg said graduates who earned the least will pay less than now.